A lightweight solution: Power chimp with rechargeable AA batteries coupled to a Powermonkey Extreme. It's a neat package with tips to recharge tablet, gps, smartphone, ipod etc.
The solar panel trickle charges as you go along and when you find mains you can recharge the 9000mah lithium polymer batttery. The solar cells will charge up to around 85% ish to the battery- after that you need the mains to 'push' the remaining charge in-Good kit.

linky