Zippo Products Hand Warmer
These hand warmers are the real deal for winters and outdoor activities. The hand warmer is a small metal rectangle that fits inside a fabric pouch. The rectangle opens at the top and contains a small plastic filler cup -- you fill the metal container with lighter fluid, and light it, then snap it shut. The flame inside warms the metal, staying nice and toasty through outdoor winter bonfires, skiing, cold hikes, and beyond.
It's compact, slim, and light to fit in your pocket -- so you've got your own little (very) mini fire to keep you warm.
Photo courtesy of Food52