While there are some devices out there that can get juiced up by the sun using solar panels, that's really not all that convenient. What about when you're inside? When it's cloudy? There's got to be an even more convenient way.
There is! It's the power shirt, a shirt infused with nanotechnology that's able to get power from the basic movements of your body, transferring that energy to the gadget of your choice. It's still in the early stages of development, but eventually you might be wearing shirts with USB jacks built in, intentionally walking briskly to keep your cellphone from dying. The future is so crazy!