Easy Energy makes a device called YoGen Max that allows you to charge your laptop - anywhere - by rocking your foot on a 'manual sewing machine' like pedal.

The device can be folded in to a compact 'box' form factor to facilitate easy portability.

It can also hold 12 rechargeable AA batteries, if you want a break from the foot action.  It produces around 60 to 80 Watts of power, enough for most laptops.

Here is a video demonstating the YoGen Max from Easy Energy.