I always used the Hot Hands, also. They work, to a point. Once your hands get used to the temp they put out, they go back to being cold. I always had to pull my hands out of my pockets and let them cool off in order to feel the heat coming off the Hot Hands.
I just recently got a pair of these for my birthday. Absolutely awesome!! actually had to turn them down to medium last week! Inexpensive, rechargeable, battery lasts all day on high, and available at Home Depot. I would highly recommend.
https://www.homedepot.com/p/Go-Warmer-17-06-BTUs-Battery-Powered-Rechargeable-Personal-Hand-Heater-with-Flashlight-2-Pack-GW2PK-MC6/317875659?MERCH=REC-_-searchViewed-_-NA-_-317875659-_-N