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.
Mine tend to be AAA models, which works out since I also often have pen lights around.
One thing I have done in my car is attach a rigid MOLLE mount on the sunscreen and then put pouches with a pen light, small knife, lighter, and pens. The kinds of things you always need and often carry but sometimes aren’t quite sure where they have fallen.