Historically, neither plane existed until 2008
D&D went without these planes for 30 years; they were invented for 4e’s wildly simplified ret-con of the planes. The Shadowfell combined the Plane of Shadow and the Negative Energy Plane, while the Feywild combined a greatly-expanded Plane of Faerie with the Positive Energy Plane. Moreover, before 4th edition, Faerie was just an idea for DMs, and prior to 3rd edition, the Shadow was just a demiplane.
So far, 5e has two uniquely Feywild/Shadowfell things
Thomas Markov’s answer lists everything in 5e that has an explicit reference to these planes—and literally all but two of the list items predate the existence of these planes. (The two exceptions are the harengon and the Hexblade warlock patron; see below for details.)
(The other caveat is that 5e’s system of “subclasses” isn’t really something that prior editions of D&D did, so there wasn’t usually a “warlock of this” or “druid of that,” so older editions’ content isn’t going to be exactly the same. In many cases, however, subclasses were, in 3rd edition, “prestige classes,” which were special classes you had to multiclass into after meeting certain requirements. In other cases, it’s more of a stretch, and I’ll readily admit my match for the druid’s Circle of Dreams is weak.)
Fey without the Feywild
Fey creatures have always existed in D&D, even when a dedicated plane did not. They were generally associated with the Material Plane rather than any other plane. This is particularly true of 5e fey, because the 5e fey designation is broader than it was in past editions and includes what had once been known as “native outsiders”—the Material analogue to celestials and fiends. 5e turned these creatures into fey and moved several of them to the Feywild. So if anything, these had more prominence in a typical (Material Plane) campaign prior to the introduction of the Feywild. Fey-based warlocks and rangers absolutely existed without it.
Specifically, to quote Thomas:
Bards date back to the ’70s, and have always had a strong association with glamours. The 3rd-edition bard had a feature to captivate an audience by default, for example, that was very similar to Enthralling Presence. Precise analogues to Mantle of Inspiration, Mantle of Majesty, and Unbreakable Majesty are harder to find, however.
On a flavor side, 3rd edition also had a couple of prestige classes for nature-themed druid/bards, the Fochlucan lyrist and the green whisperer. More notably, perhaps, is the troubador of stars, who performed in the Court of Stars for the eladrin—who are named specifically in the College of Glamour. (Then again, eladrin were very different.)
Dream-magic has always existed in D&D, and the druid has long had access to some of it. That said, I’m not sure there was ever before a specific druid dedicated to it. There was an earth dreamer prestige class in 3rd edition that druids could qualify for and benefit from, but so could pretty much any other spellcaster. Also, as the name suggests, there was a heavy earth theme that the Circle of Dreams doesn’t have.
- Circle of the Shepherd Druid
Druids have always had a strong summoning theme, and their summons have always included fey creatures. The 3rd edition druid was basically the same as a 5e druid, except that they had all of the core circles at the same time—plus Shepherd, which was for a while the one the 5e druid was missing.
- Arcane Archer Fighter, Banishing Arrow feature
Arcane archer was literally a 3rd edition prestige class, and had banishing arrow.
Rangers, like druids, have always had an association with the fey. For more specific material, there was a wildrunner prestige class, which at the end of the class turns you into a fey, but otherwise it’s more elf-themed than fey-themed, and it’s kind of a combo ranger/barbarian than pure ranger (ranger is the easiest way to qualify for the class, but then it revolves around a similar-to-Rage-but-Dexterity-based ability).
The debut of warlocks as an independent class in D&D was in the 3rd-edition Complete Arcane, and even then it noted that many warlocks got their powers from pacts with fey creatures (this version of the warlock didn’t actually get different powers based on who their patron was, though).
The degree to which elves are or are not related to the fey varies considerably across D&D history and campaign settings. But suffice to say it’s been a thing, at least kinda-sorta, for a long, long time.
Elves were also in the original 1977 Monster Manual.
See Elf. Half-elves were also in the original Monster Manual.
Satyrs also appear in the very first Monster Manual from 1977.
More entries from 1977. Note that prior to Monsters of the Multiverse—that is, even in 5e—goblins, including bugbears, were not fey.
And again with the original Monster Manual, and again with things that weren’t previously considered fey.
In real world folklore, changelings are fey creatures that are substituted for kidnapped babies. This idea—often with the name “changeling”—appears in D&D from time to time, but were never a major monster.
And since 3rd edition, “changeling” in D&D has referred to the Eberron race, which then traced their shape-changing abilities to their doppelganger heritage, and were completely unrelated to fey. But now Monsters of the Multiverse states that these changelings “first appeared in the Feywild, and the wondrous, mutable essence of that plane lingers in changelings today—even in those changelings who have never set foot in the fey realm,” which is a rather serious ret-con of the race (and appears despite the fact that Eberron: Rising from the Last War associated changelings and doppelgangers in its introduction of Eberron’s new races on page 5). For my money, Monsters of the Multiverse should be ignored with prejudice on this subject.
Either way, even Monsters of the Multiverse explicitly embraces changelings who have never personally seen the Feywild.
Eladrin are, to my mind, probably the biggest travesty in Wizards’ ret-conning of D&D’s lore. Originally, they were the “exemplars” of Chaotic Good, creatures made out of literal, incarnate Chaotic-Good-ness. That is, they were Celestials, not Fey. This made them cognate to, say, LE devils or CE demons. Their elf-like qualities were largely coincidental.
Then 4th edition for reasons unknown didn’t have elf as a playable race in the original Player’s Handbook, and instead had eladrin, who were now elves but not called “elf” for some reason. That edition got an actual “elf” later, but that honestly only added to the confusion.
And now in 5th edition, elves are back where they should be, but eladrin are fey now. Since 5e doesn’t have the “outsider,” and other exemplars (the LN exemplars, modrons) have occasionally been messed with in similar ways (modrons are not constructs, however construct-like they seem). This seems to indicate that what were previously known as “outsiders” can, in 5e, be labeled as types we don’t ordinarily think of as outsiders. Maybe.
You can see some of the fallout from this nonsense in the Forgotten Realms Wiki entry for eladrin, which splits into four different options:
- “fey eladrin” are the 5e ones
- “eladrin-as-another-name-for-high-elf” is the explanation for 4e
- “noble eladrin” are a reference to 4e-era high-elves-who-lived-in-the-Feywild, which would become the “fey eladrin” in 5e, I guess
- “celestial eladrin” are the original pre-4e celestials
None of these terms are clearly delineated in the official books; this is just the Wiki’s attempt to navigate the fact that the word “eladrin” keeps getting redefined.
Anyway, point is, the eladrin have certainly existed for a long time, dating back to 2e, but they keep changing what exactly they are.
D&D has had all different kinds of “fairies”—brownies and pixies and sprites—for decades, though it is astoundingly difficult to search for just “fairy” because that’s usually a synonym for “Faerie” (which D&D has used as the plane) and “Fey” (the category that includes all of these creatures). It may be that until 5e, D&D avoided using “fairy” to refer to any one creature, since there were so many different kinds of “fairies.”
Still, the general concept has been around forever. The 1977 Monster Manual had brownies, pixies, and sprites.
More stuff from 1977. As noted under bugbears, goblinoids weren’t considered fey until Monsters of the Multiverse. Even 5e goblins weren’t fey until that book.
@Groody the Hobgoblin reports an interview with Chris Perkins in which he states that the harengon were originally created by one of the other authors of The Wild Beyond the Witchlight, so “harengon” per se seem to be 5e originals.
As for the more general concept of rabbit-people, that might also be new but it’s very difficult to determine this for sure. I haven’t managed to find any references to rabbit-people in D&D before 5e, but absence of evidence is not necessarily evidence of absence—there might be an obscure rabbit-folk race out there buried under all the 5e results.
Still, D&D has had animal-people from the beginning; the fact that “rabbit” might not have been used before doesn’t necessarily mean much here. If the Feywild didn’t exist, it would be trivial to give the harengon a new home.
As with the goblin and bugbear, hobgoblins have been around since the beginning, but weren’t considered fey until Monsters of the Multiverse.
Originated in 3rd-edition’s Fiend Folio, and they were fey then, too. They were always native to what was then the Plane of Shadow, however.
3rd edition had a Fey Legacy feat that granted, among other things, the ability to cast dimension door.
3rd edition had both a Fey Bloodline feat and a Fey Heritage feat; both had the same idea.
Shadow with a limited Demiplane of Shadow
Shadar-kai also predate the Shadowfell, debuting in the 3rd-edition Fiend Folio, where they were fey associated with the Plane of Shadow. Shadow is a long-standing part of the D&D cosmology, though its original status as “just” the largest demiplane in existence in 2e is less than it is in later editions.
Importantly, 2e had rules for what did and didn't work if you were outside the limited reach of the Demiplane of Shadow. You may want to look into these. For example, if you weren’t on a plane that touched Shadow, the shadow walk spell wouldn’t work.
Sorcerers, of course, were always (well, since their 3rd-edition debut in 2000) welcome to select shadow spells. But shoutout to the shadowcraft mage, an incredibly broken 3rd-edition prestige class that did ridiculous things with the powers from the Plane of Shadow.
3rd edition also had a shadowcaster class. It was... weird, and not very good, and not, actually, related to the Plane of Shadow really?
Hexblade is a 3rd-edition class (an awful one, but it exists). It actually predates the warlock, which debuted 11 months later, so of course it has nothing to do with warlocks, and isn’t involved in any kind of pact making, whether as patron or beneficiary. The 3rd-edition hexblade didn’t really have much of anything to do with Shadow, either, though there was a really cool “alternative class feature” for them called Dark Companion which created a shadowy figure that debuffed enemies’ saving throws with its mere presence. (It couldn’t actually do anything, it just stood there being shadowy and menacing and creatures around it took penalties on saving throws.)
The “mysterious entity […] that manifests in sentient magic weapons carved from the stuff of shadow” that is the actual 5e Hexblade patron doesn’t appear to have any pre-5e analogue, though the concept of sentient weapons certainly does, and “The mighty sword Blackrazor” that Xanathar’s Guide to Everything calls “the most notable of these weapons” was a major plot element in the 1979 adventure module, White Plume Mountain. (It’s perhaps most famous for appearing in the computer game Baldur’s Gate, though this is considered something of a non-canon appearance and White Plume Mountain was set in Greyhawk while Baldur’s Gate is in the Forgotten Realms.)
Covered above under fey, originated in the 3rd-edition Fiend Folio but were always associated with the Plane of Shadow.
The list of shadow-themed 3rd-edition feats is long, and includes Shadowbound and Shadow Heritage, which are both quite similar. There was also the “shadow creature” template, which is perhaps even closer.
Also, bonus, Darth Pseudonym pointed out that we have
- Ravenloft, the Demiplane of Dread
which per Van Richten’s Guide to Ravenloft is in the Shadowfell. Just ignore Van Richten’s—on this, and really on most things—the Demiplane of Dread, like (nearly) every other demiplane, belongs in the Ethereal Plane. Though, to be fair, it barely matters in this case, since you certainly cannot leave the Demiplane of Dread to go exploring whatever surrounds it, whether that’s Ethereal or Shadowfell. Technically, you can enter it that way, but that’s madness of the highest order, and no one should ever, ever do that for any reason.
Conclusion
Just about everything 5e associates with the Feywild or Shadowfell, are in fact older than both of those planes. The Shadowfell “is” the former (Demi)Plane of Shadow, and some of these things (shadar-kai, spells like shadow walk) really are from there or rely on that plane, so those would be out. But for the Feywild, D&D has had fey all over the place for ages prior to there being any Fey-dedicated plane, and it was fine. Many of the Shadowfell-associated beings are likewise. Thus, I would suggest that nearly everything associated with these planes would still exist in D&D without them, just found in other places.
The only things I really can’t find anything comparable to are harengon, the Hexblade, and Circle of Dreams druid. But all kinds of animal-people are found throughout D&D, long before the Feywild, and dream-magic has been there from the beginning, there just didn’t happen to be a druid dedicated to it. The Hexblade, as in the mysterious entity somehow behind sentient weapons, that could of course be anywhere else, but also hexblade warlocks could just as easily be based on any sentient weapon, rather than some “mysterious entity” that’s associated with all of them.
