Put this tubular object in your backpack, and you can generate juice for your cellphone — just by walking around.
The nPower PEG (short for “personal energy generator”) contains a weight, a spring, some inductive coils and a battery. Put it in your pocket or your backpack, and it wiggles around with your body’s natural movements. As the internal weight moves, it generates electricity in the coils, which gradually charges up the battery. You can then transfer that power to your phone or iPod via a microSD port and an adapter cable.
http://www.wired.com/gadgetlab/2011/01/body-power/