I keep jumper cables in each car, a really nice set of 16' cables in the garage at home, and a jump battery. The battery is left over from a time before I had dummy bells on all my cars for the lights being left on. It is also handy for occasional outages; I can charge a cell phone, listen to the radio, and with an inverter I can run a fan and a CFL bulb for a few hours.

Of course, with all these wonderful things the last time I needed a jump I was in a rental truck and had nothing with me.