To make a heating pad you'd need leather, string, and something to fill it with. Usually that'd be rice but since that's not in the game the recipe would use cherry or olive kernels (plum kernels are probably too big). Put the finished pad in a hot fireplace to heat it. Leather does not catch fire and burn very easily, but if left in too long it will turn to ash.
Uses are to add Soothing Heat to various wounds such as bruises or punch sore. Or new wounds could be added.....maybe muscle strain from doing hard work for a long time like plowing a big field by hand...??