How can I keep my cooler cold longer without spending money?

Pre-chill the cooler by putting it in a cold garage or filling it with bagged ice for an hour, then dump it. Use block ice (frozen jugs of water) instead of cubes—it melts slower and gives you cold drinking water. Fill empty space with towels or newspaper to eliminate warm air pockets. Pack a separate day cooler for drinks so you don’t open the main one until needed, and pile a blanket or sleeping bag on top for extra insulation.