Short trips, nothing. Long trips (like Buffalo NY to Mopar Nationals)? Well, spare rotor and cap, a couple ignition wires, duct tape, safety wire, basic tool box with screw drivers, sockets and wrenches. Usually all tools needed to change alternator, starter, tire, etc. I'll also carry a small coil of 12 ga stranded wire and electrical tape. For fluids, a quart or two of oil. Maybe a gallon of water. And a AAA card with long distance towing.