[Everything USB] Inflight Power has a slick new adapter that you plug into the headphone jack on the airliner that can power and charge your USB devices. At only 12 ounces, it won’t take up lots of the meek space you are allotted for carry on. The adapter works by allowing a trickle charge from the headphone jack to build up over about 3-5 minutes inside the adapter.

This is a pretty cool little adapter - if I was on a plane more often, this would be crucial.