There are many variables that can affect the length of time food or beverages will stay cold. These include the ambient air temperature, the temperature of the contents at the time of packing, the volume of contents packed, and the amount and/or type of ice or ice packs used.
Cool contents beforehand
The colder the contents are at the time of packing, the longer they will keep their temperature. For example, dense frozen foods stay cold or frozen longer.
Fill your cooler completely
The fuller your cooler is with food, the longer the contents will retain their temperature. In performance tests, coolers that were fully packed produced optimal results.
Use ice packs
Ice packs or ice substitutes with a lower freezing point are preferable because they minimize the amount of condensation that can occur on the bottom of your cooler (i.e. dampness that is caused by the cold air from the cooler meeting the hotter ambient air). Ice packs or ices substitutes can also focus the cold better than loose ice cubes.
Pack your ice or ice packs in the right location(s)
As warm air rises and cool air falls, place ice, ice packs or ice substitutes on top of the cooler contents for best cooling results. When traveling you may substitute ice cubes in resealable plastic bags for ice packs.
Keep your cooler sealed
Keep the cool air inside your cooler by only opening it when you need to and leaving it open only as long as it takes to remove your food and drinks.
Pre-chill your cooler
For best results, pre-chill your cooler with ice the night before use. Block ice is preferred as it melts at a slower rate than standard ice cubes.