Supplying power using a small battery is a problem for many scientists, engineers, and designers.
I have this philosophy that is a driving force for creating new things, it is to try to make as many uses as possible out of something before giving up on it. For example, a grocery store bag being used as a trash can bag, save money and help with the environment, plus feel better about the expensive ice cream I splurged on.
Power supplied by static charge, or motion by user is the principle. Imagine someone jogging with an iPOD, and the motion from their jogging is converted into power for their iPOD. The power could be created by harnessing static electricity from their clothing, perhaps having a rechargeable battery in their shoe (to which a small string or wire could be attached to power or re/charge another device). It is also possible that solar power could be harnessed to produce such a garment or otherwise device that can sustain and/or replenish energy.
Maybe plugging your cell phone into your hat may get it the battery it needs. I know it may seem ridiculous in some ways, but it shouldn't seem ridiculous in the sense of possibility at least. One way I can understand it seeming odd is because power sources normally are seen as unsightly, big, and in the way, it may seem like it would look really bad, but it's very possible to make this using a sleek almost undetectable design that's not bulky, yet still durable. You wouldn't want it completely undetectable anyway, or no one could detect where to plug anything into it or hook anything into it.
One simple application this could be used in is a development of illuminating clothing. Where the electricity is supplied, perhaps controlled as well for timed lighting to create the illusion of motion, without having to worry about the battery dieing any time soon.
Electroluminescent lights demonstrated (in shirts past the middle of the video)...
Another possibility, that I'm not really very keen on, is the possibility to harness energy from human power, for example, the excess energy we have. Is it really excess? Or is it a mandatory and necessary amount of energy that must be allowed to be excess? E.g. Carbon Dioxide and humans. Without CO2, plants die. Without plants, there's no oxygen, without oxygen, well, we need that to breathe.
Let's end this article on a good note though!
Perhaps someone should make something to make use of energy we have on us. We all gather static electricity, instead of letting it zap us, let's use it!