Ok, as promised, here is the how-to on the foot warmer inserts. I didn't do pictures with this one, as it is fairly simple. If anyone wants pictures, let me know, and I will gladly take some.
What you'll need:
4 7"x14" pieces of muslin
2 lbs of rice
A wide mouth funnel(this makes transferring the rice into the bag really easy, but you don't have to have this)
Place two pieces of muslin right sides together, and sew 1/4" - 1/2" away from edge on the two long sides, and one of the short sides. Turn right side out, and press down the opening about 1/4"-1/2". This will make sewing it shut a lot easier!
Pour 1 lb of rice into the bag and shake it all to the bottom. Sew opening closed.
Repeat with remaining muslin and rice. These should fit nicely into the pockets of your foot warmer cover.