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.
Hand sanitizer and a small bar towel for if anything needs a light cleaning.
You should never forget where your towel is.
That’s a guy that knows where his towel is.
The towel is a smart idea. I used to carry around a handkerchief for stuff like that (and if I needed to blow my nose while I was out and about).