Comment To answer the question (Score 1) 696
I use a Zip-Linq USB multi-head charging cable. About $10 most places, and you can get heads for just about anything. Fits in a very small bag.
Currently I charge with it:
Nintendo DS
PSP
Nokia e61i
Nokia LD-1W GPS
Bluetooth headset (anything with USB Mini-B)
iPod 5th gen (anything with standard USB)
The power source is either a laptop, desktop, cigarette lighter USB adapter, or a USB wall-power converter.
http://www.pcaccessories.org/ZipLinq-USB-Cell-Phone-Charger-I/M/B0000UI2KU.htm
I had to order the e61i head, model "NK2", from the mfr, but that was easy enough. I also have a 9-volt booster tip; I believe the charger itself is 5v.