Something like this? http://www.amazon.com/dp/B003ZBZ64Q
I have that one and it works great. It suits me fine for a weekend trip without power.
I have used that in the past the only thing with these power pack is that it takes a long time to recharge. Unless I have a solar panel that could recharge this then we are talking of something reasonable. Good product though I use to run my tablet on this for hours when I was living abroad.