The nPower PEG charger "harvests" your kinetic energy as a source of renewable power, allowing you to keep your phone or other small device running while away from outlets. Running, biking, or even just walking will keep the electricity flowing.
By placing the nine inch tall nPower PEG in your bag vertically, it will begin to charge its internal battery once you start moving, handing off that energy to your device(s) as needed by way of one of 100 interchangeable adapters. Tremont Electric, the PEG's manufacturer, recommends fully charging it (via USB or AC adapter) before leaving home, and then using the kinetic harvesting to "top off" the battery on the go. This makes sense, as the electrical yield on your skipping and stomping isn't exactly generous: about a minute of iPhone 3G talk time from 10 minutes of walking, or one minute of MP3 playback from one minute of walking.
At any rate, having an essentially limitless (so long as you're patience doesn't run out first) source of power away from home could be invaluable, whether for shooting off one last inane text or making a lifesaving phone call in the wilderness. While the notion of having anything harvested from you might give you the creeps, just think—you were going to waste all that perfectly good kinetic energy anyway. [nPower PEG]