FOR MOM: Rice Heating Pads. Great tutorial and materials list. perfect for neck or for lap/back. I've made similar heating pads, but I like the divided sections on these pads. They probably form to the body better.
DIY Rice Heat Pack - Easy Do It Yourself Heat Pack Tutorial Made With Rice - Cheap and Quick DIY Projects for the Home, This Craft Makes an Awesome DIY Gift Idea for Christmas Presents - Modern Crafting
Tutorial: How to sew a Rice and Lavender Heating Pad