Cook Pot of Concealment. Any edible item in the pot is invisible to a creature that could eat it until removed.
Book of secrets. When opened, the book displays a secret whispered in the last minute, at least 50 miles away, somewhere on this plane.
Ring of magic detection
As an action, you may use this ring to discover the location of the nearest magic item.
spoiler
The nearest magic item is always the ring itself.
Something with a very niche useage like a Wand of Ring Detection; starts with 4 charges and regains 1d4 charges at dawn, expend a charge to become aware of any and all rings within 30ft.
Would usually be useless, until the one time you can use it to recover a lost/stolen ring or become aware of someone hiding their powerful magic item!
Or when they start using it at random and become aware of random little trivia of NPCs around them!Also, chain mail would be obnoxious to someone using the wand!
And its counterpart, the ring of wand detection.
Ring of Luck.
Note this is not Ring of Good Luck.
Implement it as you wish. I currently flip a coin at the start of each day, and depending of that, it’s good or back luck for the day. Never communicate which, let the player using the ring find out.
Ring of attunement: allows one additional item to be attuned for the player (requires attunement)
This is actually really strong for a max level artificer as they get a +1 to all saves for each attunement
I wouldn’t say “really strong”, but +1 on saves due to a lil’ trick is neat!
One of my players really enjoys his Cloak of Billowing
Boots of blinding speed.
Reference, in case you’re not an old.
A bench which increases your intelligence to 30 so long as you’re sitting on it. It isnt so heavy that it can’t be picked up, but it is quite cumbersome
Thinking Stool
An idol that periodically tells the current time of the day in a loud and clear voice. But only at night (or when the party likes to sneak).
I gotta say, that’s a pretty good useless item
Deck of too many things, it’s a deck of regular playing cards that constantly vomits playing cards when opened.
I always try to have 2 Immovable Rods with my character so I basically have an infinite ladder. You can lock and unlock each rod and use them like rungs to climb things, cross gaps, etc. And they’re not really rare or expensive.
Maybe add the opposite of those; rods that never stop moving. Unstoppable Rods.
The vibrator of slicing.
This is a knife with two saw-like blades that move back and forth, allowing enhanced slicing of cooked or raw meats.
It gives advantage on all intimidate checks, with a +2 if wearing fishnets and/or high heels
