I love the idea of a non electric heating pad.  This is a very simple project for any begging sewer.  You fill a pillow that you make with rice and you could also put pretty smelling herbs in it too.  You can add your favorite herbal tea with the rice.   You can make one several different ways.  The Tangled Nest made one with a kind of envelope to put the pillow in as a cover  preferably from some soft fabric like fleece.  Then when you are done to use it you heat the rice filled pillow in the microwave and place back into it's envelope.  On the blog the Magic Onion they used an old cashmere sweater and she used the sleeve to make a pocket and filled it with rice and tea.  When finished take the cover off to heat the bag in the microwave for 1-2 min depending on your microwave.

Felted Cashmere Aromotherapy Heating pad tutorial at the Magic Onion

You can add herbal tea to the rice for a nice aromotherapy heating pad like they did at the Magic Onions.

tutorial from The Tangled Nest.