Coolers serve as portable refrigerators when going on picnics. These tips will help your coolers—and the items inside—stay well-chilled for the duration of your outing.Cold foods (especially those containing mayonnaise) and beverages should be thoroughly chilled before being put in insulated coolers.Beverage coolers tend to be opened frequently during a picnic. So use one cooler for beverages and one for cold food.Transport hot food in a separate insulated cooler. Wrap the hot items in newspapers or dish towels, then pack the dishes tightly in a cooler lined with dish towels.Prechill coolers by placing a few ice cubes inside and closing the lid about an hour before filling. Right before you leave for the picnic, pack the cooler in the opposite order of how you’ll be using the items. That means the foods you need first should be on top, so they’re easily accessible.Put blocks of ice or ice packs on the bottom of the cooler. Layer with food or beverages, then top with ice cubes or crushed ice.A full cooler will stay colder longer than a partially filled one, so pick the right size cooler. If your food or beverages don’t fill the cooler, add more ice.Don’t put coolers in a hot trunk, especially if traveling quite a distance. Put them in the backseat of your air-conditioned car. Surround with blankets, sleeping bags and clothes to insulate even more.While at the picnic, keep coolers in the shade, cover with blankets and keep the lids closed as much as you can.If possible, replenish the ice as it melts. If you don’t have access to more ice, don’t drain the cold water from the cooler…it keeps things cold almost as well as ice.