A better way is to buy fresh orange juice in plastic or carton 1/2 gallon jugs, open them up, drink a little bit and then freeze the oj jugs solid...
Place the oj jugs (with caps on) in the bottom of the cooler and cover them with ice.
Orange juice has a melting point that is colder that water's melting point, so first the ice melts, then as the oj melts, it re-freezes the ice... and the cooler goes through this melting refreezing process for a while... you will be amazed how long this will last... just make sure your food stuffs don't freeze into the water that gets refrozen...