My daughter came up with these for her projects to sell in her classroom.
You will need,
cloth, soft, like flannel, cut 5" wide by 12" long
1 Large bag of rice (buy from the dollar store) its cheeper
thread to match material
Sew 1st long side then the other, then the bottom end, turn the bag inside out, then fill with rice, but leave about some room to sew the top by your sewing machine, then turn the edges inside the bag for a nice hem, sew together, and that is how you make it. It freezes as well as put into the microwave for heat.
Great little project.