I carry a couple spark plugs, 2 qts of mobil one, a belt, small vac line and a bag of misc tools. I don't even have a spare tire lol it went mysteriously missing last week.
AAA card, flashlight, seatbelt cutter, window hammer and a fire extinguisher. Anything else is useless, IMO. If it isn't on fire or sinking in a lake, I'd rather just have it towed home and fix it right. Very rarely is it going to be something that can be fixed enough to limp home, anyway. I don't half-ass break things. I shatter transmissions, burn up ignition parts, and puke coolant all over the street.
Air pump, tire plug kit, warning triangle, medical kit, chem lights, hand warmers, jumper cables, a couple of quick fixes for the car - little things that commonly break.