First and foremost, make sure to completely empty the cooler before cleaning it. At a minimum, remove all the water and melted ice, and then wipe it down before storing it away. If the cooler has acquired some dirt, debris, or stains after a more lengthy adventure, use a mild detergent, such as dish soap, along with a sponge and water. For tougher stains, a diluted solution of baking soda and water should erase those spots. If the cooler retains an unpleasant smell, spraying some bleach, and then wiping it off with water should do the trick. If it still has an odor, try wiping it down with vanilla extract and washing it with water again, and then allow it to air-dry. If the cooler has a drain plug, make sure the valve is open to allow any trapped moisture to escape before you stow it away. Soft coolers can be spot cleaned or wiped down with mild detergent and water, but do not put any kind of cooler in the dishwasher or laundry machine, as that will likely ruin it.