Heat packs that do not requre a microwaves?

Are there any heat packs that dont require a microwave? We haven’t had a microwave in years and if like to get a heat pack to use on ingrown hairs and back pain. Anyone have any that dont require a microqave?

Yes hand warmers in the sporting goods section

Or they have those ones with the metal disks u click and to reactivate u boil in water on the stove

They have these on amazon. They work great, you bend the disk in them and they get hot. When done using boiling until liquid again and they are ready to use next time.

Could you make/use a homemade rice pack and put it in the oven on a very low temp to heat