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.
Band-aids. They fit easily into your wallet, taking almost no space. You’d be surprised how often you use one, either for yourself or someone else.