If you live in or regularly travel to a cold climate then I strongly recommend HeatMax’s HotHands.
I bought a package of these last Autumn to keep in my car for emergencies. I didn’t try them until last Saturday, when I was camping in the mountains.
A rainstorm soaked me with cold water and changed the air’s temperature from Comfortable to Unbearably Chilly. Even with a borrowed winter coat over three (or four, depending on the count) layers of clothing, I wouldn’t have been able to continue hiking if not for a HotHands-2® hand warmer.
Though the little packet is about 3.5″ long and 2″ wide, and didn’t feel as hot as I’d expected, I missed the warmer anytime I handed it to someone else. I immediately noticed my body temperature drop, as if I’d removed a coat. The return of the warmer was like putting on a coat again.
Except, the HotHands warmer was better than a coat, because I didn’t have to create my own heat; the warmer supplemented what I produced. I’ve learned that makes a huge difference when you’re cold to your core.
The HotHands-2® warmer I used lasted about half a day. I actually slept with mine zipped inside a pocket, despite a warning from the manufacturer not to sleep with it. I slept through the night, thanks to the protection of the little packet.
A supply of these will be forever maintained in my family’s vehicles. I’ll also keep at least one HotHands product (possibly a foot warmer with a hand warmer) in every coat and jacket I own.
By the way, they are inexpensive, nontoxic, and (where I live, anyway) available in most stores.