I saw that it can create trinkets that can fit in your hand, and I wondered what qualified as a trinket?
Anything that would be called a trinket in normal English usage.
One such definition is:
1: a small ornament (as a jewel or ring)
2: a small article of equipment
3: a thing of little value : trifle or bauble
Trinkets as defined in the Trinkets Table serve a different purpose. They are explicitly called out as items used for character creation, or odd treasures to be found. They are items of mystery, and generally not suitable for something which can only last 6 seconds. There is no link between them and the spell usage.
Furthermore, many items on the table can not be used as part of the spell, as explained below. There is no reason that such a large variety of objects of various sentimental and real value would be considered valid for something which the spell defines as "a non-magical trinket or an illusory image that can fit in your hand and that lasts until the end of your next turn." (PHB p.267)
For example, could a music box be considered a trinket? Why, or why not?
A functioning music box would not be considered a trinket. However you could replicate that with multiple castings of the spell. The music box created by the Tinkerer Gnome, for example, costs 10 gold and 1 hour to create. 10 gold is more than most items cost.
The spell lists multiple effects the spell can have and lists them as an exclusionary list (only the effects on the list may be done). It also allows for up to three effects to happen, if the spell is cast 3 times.
One of the items on the list is to create a harmless sensory effect, such as faint musical notes in the air. Another separate affect is to create a any illusory image in your hand. (PHB first printing, p. 267)
So while it is clear that you can create the image of a music box, it is not clear that you can create a functional music box with only one casting of this spell. And even then, it appears that the musical notes can only be faint.
If you wish to temporarily create a music box, you are better off using the Minor Illusion spell which specifically allows you to make sound and images together.
I know there is a trinket section of the book, but surely you couldn't make everything from that list?
Correct, see below for a full list of items on the list that can not be cast with the spell.
The section on trinkets reads (p. 159 Player's Handbook):
When you make your character, you can roll once on the Trinkets table to gain a trinket, a simple item lightly touched by mystery. The DM might also use this table. It can help stock a room in a dungeon or fill a creature’s pockets.
The trinkets section of the equipment guide is unrelated to the spell. This can be surmised from two key facts.
- Trinkets are defined with a unique definition in the equipment
- The spell does not make reference to the table.
The following items from the table fit the PHB definition of a trinket, but not the normal definition and can not be produced with the prestidigitation spell. Either because it makes no sense for a spell which lasts 6 seconds (e.g. The items which cause dreams while sleeping or the ring that never tarnishes), can not be discerned to be the item that you created (e.g. A candle that can't be lit, or the lump of coal which you claim looks like a gemstone to you.), contains implicit magic (e.g. The weightless stone block), or is just too large to fit in the hand (e.g. The vest or scabbard). Some items might be able to be passed off with a deception contest (e.g. The knife belonging to your relative, or the lump of coal which you claim looks like a gemstone to you.):
04 A diary written in a language you don’t know
05 A brass ring that never tarnishes
A small idol depicting a nightmarish creature that gives you unsettling dreams when you sleep near it
21 A tiny gnome-crafted music box that plays a song
you dimly remember from your childhood
A shard of obsidian that always feels warm to the touch
A blank book whose pages refuse to hold ink, chalk, graphite, or any other substance or marking
A knife that belonged to a relative
A rectangular metal device with two tiny metal cups on one end that throws sparks when wet
A vest with one hundred tiny pockets
A small, weightless stone block
A gemstone that looks like a lump of coal when examined by anyone but you
A mechanical canary inside a gnomish lamp
A tiny chest carved to look like it has numerous feet on the bottom
A dead sprite inside a clear glass bottle
A candle that can’t be lit
A pyramid of sticky black incense that smells very bad
A nightcap that, when worn, gives you pleasant dreams
A silver teardrop earring made from a real teardrop
An ornate scabbard that fits no blade you have found so far
A bit of folded cloth that, when unfolded, turns into a stylish cap
A diary with seven missing pages
A book that tells the story of a legendary hero's rise and fall, with the last chapter missing
A needle that never bends
A tiny mechanical crab or spider that moves about when it’s not being observed
A wooden box with a ceramic bottom that holds a living worm with a head on each end of its body
What are other examples of interesting things I could create?
Any simple item you can think of, that does not appear to have magical properties, and has no intrinsic value.