Solar Powered Vibrator
Why not have a little sexual fun while developing that nice malignant melonoma! Now instead of wasting batteries, you can fry yourself happily in the sun using nothing but the power of the sun.
I actually managed to find one of these in a local sex shop for $3, it seems to be pretty capable of driving most small vibes, though don't expect it to rock your world. You may get .5w out of this if you're lucky. However, it's always a last resort if you're out of batteries!