Fill a gallon milk jug almost full with water and cup regular table salt (leave space for the ice to expand). Pack into your cooler and it acts as an ice block that won't melt all over your food! The salt slows the melting of the ice.
Snapware Ice Block in cooler: Keeps food cold for at least three days! Great information for if the power goes out and you have a full freezde/fridge of food OR for RVing and camping! Sure beats a bag of ice that melts all over.