I carry a powerbank and various USB C adapters so if someone’s device dies I can help them out. It is a lot cheaper and smaller than carrying around seven different cables.
On top of that I carry Tylenol and bandages.
I used to carry a full first aid bag but kept forgetting to restock on supplies.
I’ve gotten a lot of keyring multi-tools over the years, but the only one I keep on my keys is the simplest: a Powerful Pete pocket screwdriver. It’s just a little metal disk with 4 different sized flathead screwdriver tips. It’s remarkably useful, I can even tighten hex socket bolts in a pinch.