The "iGo Power Extender" has been a companion for quite some time for me - simply pop in two AA batteries and plug it into the device that needs juice.
http://www.igo.com/powerxtender-char...t/ps002640004/
The thing sells for U$ 10.00 at many US airports, comes with one "tip" (adapter for one device). I need two tips: mini-USB and Apple Dock Connector and I can keep both fone and reader juiced on long flights.