I know the sock monkey handwarmers are sold out, but just wanted to say I have these and they rock!
The kids and I use them all winter long. It takes just minutes to get them into a reusable state in boiling water. They keep warm for a good 30 minutes at least; so long as they are kept in pockets. They do NOT warm up enough though if you start them out by snapping the discs if the monkeys are ice cold in the first place. I had a pair in the car over night during winter and they were chilled. When I snapped them to activate them, they were just barely luke warm. Lesson learned. Still, They have lasted us a full winter and are sitting in our closet waiting to be used again when winter comes!