Goal zero also makes a cool backpack able solar charging panel with a rechargeable battery pack that is around 100 bucks. The panel can charge the battery pack or you can charge it through a USB port. I have a couple of extra sets of rechargeable batteries and charge every thing up before I leave and recharge with the panel as needed. Some of them include a led light too which is a pretty cool light at night. I charge my iPhone and atrag PDA with it as well as using the rechargeable batteries in my kestrel.
traveling on a plane I precharge my battery pack and have two recharges for my phone on the trip.