This is another variation on the egg carton idea... My scoutmaster always had what looked like miniature egg carton shells that were about 1/2 the size of regular egg-type cartons. He said he used a mixture of paraffin, sawdust, and charcoal. The paraffin was melted in a double boiler, mixed with the sawdust and the ground up charcoal 1 to 1 to 1. The egg carton halves were then filled with this mixture and allowed to partially solidify. Two halves were then pressed together so that they would break into "eggs" when needed. The whole thing was then coated with a film of paraffin.