One recent example from a game that I ran is that my players caused a dust explosion using flour. I had to do some quick googling to figure out how big that might be to best gauge the damage (turns out it can be pretty big), but I awarded inspiration for the creativity (despite getting caught up in the blast themselves). This was also a bit of irony since the people they were attacking were assassins that ran a bakery as cover.

It didn't actually end up working, because he didn't roll quite high enough, but in our session last night, our cleric tried to use Shape Water to freeze water from a water skin into the shape of a missing gear that we needed for a puzzle

If you're interested in fun ways to use items, definitely pick up a Block and Tackle the next time you're at a general store. That's how you make Scooby Doo traps

Not DND but one time in Mage (a game of modern day magic) my players were trying really hard to contact another group. The players were in NYC and the other group was who-knows-where, but they were heavily magically warded.

After two failed and resource intense attempts to magically contact the other group, I asked if they wanted a hint. They said sure. I said, "Why don't you call them on the phone?"

Not an item, but our DM let a player dissolve a mundane door lock with the acid splash cantrip

Use and abuse prestidigitation. Annoying dog? here puppy, the best steak you ever tasted. need to ask the guards again? Change my clothes. plot exposition? minor cube of illusion. Between that and mending I have my GM debating firing my bard after only 3 sessions of curse of the crimson throne.

As an urchin background forest gnome, I tried to abuse the hell out of my pet mouse and speak with small beasts ability. Unfortunately, our sessions did not last long enough for me to come up with too much fun shenanigans.

Powdered chalk or ink or oil on an invisible creature. Throwing powdered chalk around a room to track foot steps of an invisible creature.

My rogue jammed a few door locks by cramming ball bearings into the keyholes once.

Tavern chair as a weapon count?