If you're away from power sources, what are your options. Solar, Dynamos, etc.
Amazon has pretty good prices, but the reviews are what can give you a better idea of what to expect

Amazon.com: Opteka BP-SC4000 Ultra Thin Solar Powered High Capacity (4000mAh) Backup Battery and Charger for Cell Phones, iPhone, iPod, and Most USB Powered Devices: 47th Street Photo

Amazon.com: SOS Charger Hand-Crank Emergency Cell Phone Charger with 3 LED Flashlight: Home Improvement

Amazon.com: K-TOR Pocket Socket Hand Crank Generator Portable Power Supply 10 Watts 120 Volts Made in the USA: Electronics

There hundreds of different gadgets, I read a lot of reviews and see these as pretty good choices, but I haven't personally tried any of them yet... I'm sort of leaning towards trying the K-tor hand crank generator, just seems like something cool to have just in case...

When camping, I have a spare 12v marine battery in my toolbox that I wired a cigarette adapter and extension to so I can just plug in from up to 15 yards away, runs small TVs and charges anything and being deep cycle I've never been able to kill it over a weekend.