Hey all, quick question: if a PC drinks a potion that buffs them them up (like cloud giant or the like), then goes down in a fight but is brought back up, do the potion buffs stick with them or are those gone?

We can infer that dying doesn’t relieve a character of negative conditions because only some of the spells that restore life specify that the character is relieved of them when brought back. If a character is poisoned when they die, they are still poisoned when returned to life using Revivify but they are no longer poisoned when Resurrection is used, for example. Because of this, I suggest that positive conditions persist through death unless otherwise stated (which I don’t think you’ll find anywhere but you might *shrug*); the PC would still have all their buffs when brought back up.

FWIW, while your situation hasn’t come up in my home group, we have had cause to decide spells that are not concentration cast by a character who dies last for their duration in my home group. So if the cleric gets smushed in battle, their spirit guardians goes away because they can’t concentrate on it but their spiritual weapon would keep on trucking for a full minute, that sort of thing. 

Quick answer: Unless ruled or stated otherwise, item description informs exactly how long it lasts regardless of the creature being revived or not in the meantime. Maybe some resurrection effects specify additional things, so make sure to read those, specially the homebrewed ones.