First you start with the very good Mintyboost, which you build from an Altoids gum tin. It can use any AA size batteries to provide USB charging power for phones, ipods, iphones, whatever.
http://www.adafruit.com/index.php?main_ ... ucts_id=14The mintyboost by itself can be great when very far from a grid, when paired with some lithium single-use batteries... They're half the weight of alkaline and perform great in cold weather.
But here's the cool part: Built it into an Altoids mint tin with a 2200 mAh lithium ion battery, a charge controller and a small solar panel:
http://www.instructables.com/id/How-to- ... /?ALLSTEPSIt's easy enough to do that anyone with very basic soldering experience can build one with a cheap 30W soldering iron from Radio Shack, and a Leatherman. The total parts bill is about $70.