I built a DIY FireWire-to-car-socket adaptor, and use it with a 2-port USB car charger to get an extra two USB charge-only sockets on my laptop.
Just a warning: the Thunderbolt adaptor actually outputs 16V not 12V. Thankfully most 12V devices (including iPods) accept higher voltages, usually up to 24V or 30V.
I built a DIY FireWire-to-car-socket adaptor, and use it with a 2-port USB car charger to get an extra two USB charge-only sockets on my laptop.
Just a warning: the Thunderbolt adaptor actually outputs 16V not 12V. Thankfully most 12V devices (including iPods) accept higher voltages, usually up to 24V or 30V.