Here is my solution:
Take a new clean sock, fill with rice, tie off with a hair-tie or rubber band. And put it in the freezer. {You can also heat in the oven or microwave for hot therapy.}
I love it. If it gets wet, I can open it, dump out the wet rice, wash and dry it, and start over. It is so simple and easy. And cheap because I already had these things in the house.
Beach Cheap! ;)