Here's an off-the-wall thought: has anyone considered using rechargeable drill batteries to power camp items? They're light, charge fast, and you're going to be carrying them anyway. (Though you'd want to be careful not to leave yourself drill-less.)
At about 3Ah each, I think you could run a small stereo off one for a day or half a day. Don't know how many watts you can pull - but I assume a fair number, given how quickly a drill will chew through one under a heavy load.
I know some of the manufacturers make non-drill doo-dads that run off these batteries (like flashlights, for instance). Would be cool to rig up an inverter that does the same.