One quick question Packrat.
How do you keep them from getting wet?? The ones I have are almost like a tea bag sort of material which you could rip easily. With falling snow it seems that the snow would quickly melt all over the handwarmers making them useless.
Usually when it is cold enough to need hand warmers it is too cold to snow so I have not had a lot of problems with them getting too wet. With the disposable heaters I use some medical tape that allows them to breath a bit and offers a bit of protection. I do not know how much you need to seal them off before they stop producing heat but you might be able to use a bit of plastic for a cover as long as they get some air.
I have mostly switched to the reusable warmers as they seem to put out more heat but for a shorter period of time.
It is funny how you get used to the cold as it was only -16C today and felt like a light sweater day rather than a big parka day!