I'm sticking to hand tools for my answer. I don't keep these in the car all the time but they are my most used tools I guess so thats why i'm mentioning them. #4 is porsche specific and should always have one in the car along with a spare belt.
1. A 1/4" drive set of these (6mm - 14mm). I have a 3/8" drive set of larger sizes.
2. Short and long allen sockets
3. REVERSIBLE rachet wrench set:
4. Fan pulley wrench:
5. o ring hook/picks. Good for more than just removing o rings:
6. Nice slip joint pliers:
