Truthfully, I was considering a small pistol and was worried about the ammo. I do have a CCW so it wouldn't be an issue.I keep a handful of fuses, a photo copy of my driver's license, 20 bucks, and my tool kit. I've added big, good, name brand vise grips and some real wrenches.
IMO a small first aid kit is a good idea but wouldn't be beneficial.
Having survived a few accidents, I can tell you that you'd need more medical supplies than you could fit in there. Lighter would be fine. I always advocate a knife.
Rumor has it, allegedly, a KelTec PF9 fits in there. But good luck explaining that when asked for your license and registration.