Boasting enough capacity to hold 4 large beach towels and constructed of heavy duty PVC coated materials this bag has a roll type opening at the top which clips to make it water tight. It also has a waterproof side pocket with a zipper and a signature cup holder. It can be carried by hand or worn as a backpack and can be clipped onto boat railings to keep safe and out of the way. The TackleWebs Ultimate Waterproof Marine Bag comes in two sizes 30L and 20L.