I carry a 55 piece tool set (~20 sockets, 1/4 ratchet, 3/8 ratchet, couple of screw drivers, Allen wrenches, etc.) that someone got me for Christmas years ago. Along with that, I have:
- 4D cell Maglite. It throws a lot of light and it doubles as a club if someone tries to attack me; positioned right next to the driver's seat
- 2AA cell Maglite + LED upgrade in the center console
- Crank-up flashlight in the trunk
- Jumper cables
- Duct Tape
- Small knife
- Small electronics tool set with needle nose pliers, wire cutters, etc.
- Crappy scissor jack included with spare
- A spare headlight / tail light bulb
- A couple of glow sticks (to use as "flares")
- Spare coat
- Umbrella
- Gloves
Most of the stuff is aimed at keeping me and a passenger safe if something goes wrong. If it's more than a flat tire or another simple repair, I won't be able to do it on the side of the road anyway. What little tools I carry are primarily for helping other people when I don't have time to stop home and grab proper equipment first.
The Mustang will include a slightly larger tool set (older car, less reliable, easier to get at stuff and fix), most of the same stuff, plus a gallon of water, quart of oil, and maybe a jump pack.