This $22 Zippo hand warmer will keep your hands toasty for six hours, just like those disposable Hot Hands packs. But unlike those packs, the Zippo then can be recharged over USB cord, and reused over and over again. Plus, you can use it year ‘round to charge your phone, as it doubles as a 5200 mAh USB battery pack.
Source: io9 – When Gloves Aren’t Enough, Buy Zippo’s Rechargeable Hand Warmer For Just