Old sponges can be given a second life as freezer packs. First, wet your sponge and disinfect it in the microwave by heating it on high for 90 seconds. When it is cool, soak it in water and place it inside a freezer bag. After it's frozen, place it in shopping bags when you grocery shop, and it will help keep frozen food cold longer. As the ice melts, the sponge will automatically reabsorb the water.