I just picked up a couple pairs of electric socks off amazon for stocking stuffers. one set for my wife as she always complains that her feet are cold in our house, and one set for me. 19hr battery life on low at 104-115 degrees.
I'll also be making a heated long sleeve T-shirt pretty quick too. I found a heater kit on ebay for like $12 that you simply sew into a shirt and plug in a usb power pack and it helps keep a guy warm. I may do a write up on it in case anyone else wants to try it. I know for a fact that the heater kit works as I've messed with it a bit, I just haven't sewn it into a shirt yet.