Mix the alginate with water in two buckets according to package instructions. Use warm, but not hot water to keep the alginate from setting too quickly. Unroll the plaster bandages and set them aside. Lay out a piece of plastic sheeting.
Get a friend to help you prepare your body for casting. Protect your hair with a swim cap. Trim all body hair to 1/4 inch or less, and coat hairy areas with petroleum jelly. Coat less hairy areas with hand cream.
Stand on the plastic sheeting. Have your assistant rub alginate over your body in a layer at least 1/4-inch thick. Have your friend coat your entire body, including the head, but make sure to leave a space for the nostrils. Allow the alginate to set up. It will become rubbery.
Have your friend fill a bucket with hot water and dunk a plaster bandage into the water. Your friend should lay overlapping strips of plaster over the alginate to create a mummy look.
Wait for the bandages to set. They should heat up, then cool down and become firm. This can take up to a half hour. Have your assistant cut the mold off carefully using blunt-tipped bandage scissors. Repair any damage with plaster bandages and casting plaster.