The lasagna method keeps ice the longest.

Yes, pre-chilling and layering ice between food makes a huge difference. You’re basically building a thermal battery, and every shortcut you take costs you hours of ice life.

Start cold. Chill the cooler itself overnight, or at least toss a bag of ice in it for an hour before packing. Pre-chill everything you’re putting in — warm soda cans are the enemy. Then pack in layers: ice, food, ice, food, ice. That gives you cold from all sides, not just the bottom.

Use block ice or frozen water bottles instead of cubes. Big blocks melt slower. Fill any empty space with crumpled newspaper or more ice — air pockets are ice killers. Keep the lid closed and the cooler in the shade.

You’ll still have ice on day three, assuming you don’t open it every ten minutes.