Something not too many people have, but you really like. Not like a flashlight or a knife/multitool. My most unique (although still popular) are probably my loop quiet ear plugs. They come in handy in a lot of cases and word really well.
Not sure if it quite meets the standards of the question, but I keep calfskin driving gloves in my car and I love them. They’re good for when the steering wheel is too hot or too cold, they keep my hands from getting sweaty on long car trips, and they make me feel like an old-timey race car driver.
A cheap little tape measure. It’s surprising how often it gets used.
I drilled a little hole in one of my guitar picks and added it to my keychain. It comes in handy for all sorts of things!
A fresnel lens
Mainly magnifying but it has a little ruler and can start a fire/fuse some plastics in a pinch too.
Everytime I eat certain meats I end up with food stuck in my teeth.
This has happened enough times that I wished I carried toothpicks. So now I carry a slim brass tube filled with wood toothpicks.
