Wand of Cure Light Wounds. Even if you have a mobile bandaid (read cleric) these things see no end of use.

Castle Zagyg (or the joke Castle Greyhawk adventure set) adventure has a Decanter of Endless Lemonade, whcih you lose the stupper to while being pelted by animated cream pies....

.... you can't make this stuff up

Our DM insisted on giving us things like the Decanter of Endless Urine. NOT one of my favorite items.

I prefer the utility storage items. Handy Haversack, Efficient Quiver, Infinite Scrollcase. I'd add the Belt of Many Pockets, but there's too many important uses for the belt slot, darnit.

For me it is any object that creates a random occurrence when invoked, something that just creates utter chaos and removes the PCs or DM from their "planned" path for just a little bit.

The Rod of Wonder is one my favorites, but the Deck of Many Things always tugs at my gambler heart strings.

I have found the must-have at lower levels especially is the Belt of Healing -- relatively cheap and makes anyone into a healer for up to 6d8 per day.

Had a paladin and a mace of disruption that destroyed the undead captain of an entire boat of undead that we were stuck in the middle of. Which then got rid of all the other undead that would have killed us. Very memorable.

Also - after and before that I kept losing it, having it taken away, having to get it back. Felt very attached to... well was trying to stay attached to that thing. Made it feel very valuable and sought after. Even if just by my character.

Another vote for the Rod of Ropes.

You can make it look like a cane or use it as a quarterstaff for a monk.

Nothing beats following up a flurry of blows against a pirate captain by knocking him and his first mate off opposite sides of the deck.

I have always loved the Frostband. It to me is just an evocative weapon and one I always as a player enjoyed when it was worked into a game.

I would have to agree with this especially since one of our players will loot anything that isn't glued down even down to gold plates, artbooks, and other such junk. Luckily the DM never really kept track of encumbrances/capacity else we would have been in trouble.

Hat of disguise. So much fun to use.