i decided to make these little hand warmers for valentine's day. here's how i made them:
cut a piece of fabric from an old shirt about 2" x 6" (you could make this ANY size). fold in half, "right sides" together. stitch up the sides leaving about a 1/2" gap at the end. turn inside out. with a funnel, fill with uncooked rice, about 2/3 full. fold in the un-sewed fabric, and whip stitch to close.
warm in microwave for about 15-20 seconds for a cozy treat for your cold hands! you could keep inside your mittens to keep your hands warmer when outside.

i plan on making bigger ones soon for cuddling in bed!