This is the first time I've DM'd 5e (returning from extensive 2e and 3e experience).
I've run the group through the official "Lost Mines of Phandelver" adventure and just started the "Hoard of Dragon Queen" adventure. All potions the group has looted/purchased have been used since healing ability is a scarcity in this group (Paladin, Sorcerer, and Ranger/Cleric). I only allow long rests outside of active dungeons (Alarm spell goes off alright!).
When the ranger multi-classed as a cleric, she realized she could cast Goodberry with all available unused slots before a long rest. This way, she would have them for the majority of the next day. We are only level 7 now, but I can see the impact of Goodberry getting out of hand (i.e. expending multiple slots with a lot of healing on tap, effectively negating short rests). (I don't allow Goodberry to be used to revive unconscious characters.)
Now, I've found that small brawls/encounters are trickier since the party effectively has pockets of Cure Light Wound on tap (plus the full reserve of cleric/ranger slots). Even the fact that it takes an action for every HP of healing doesn't fully counter this.
The Problem With This:
As you can see Goodberry has changed encounter dynamics — the group can start a dungeon with 100+ HPs of targeted easy healing (only gets stronger as they level).
Hoarding spell slots isn't the problem (wouldn't be an issue in my eyes, this would mean they'd have to not cast spells in other situations). The problem is the prospect of a safe long rest starting with the previous night's Goodberry hoard. To solve this problem, I came up with the following house-rule:
"Goodberry will last 24 hours or until the caster regains spell slots"
This way, you can cast Goodberry before sleeping and it will remain in effect if your sleep is interrupted, but after a long rest it will lose potency (and your spell slots refresh).
Is this a balanced rule change? I cannot find other spells in the PHB that have a similar duration of >8 hours and don't require concentration or active spell slots to compare it with (perhaps Goodberry is a one-of-a-kind spell?).