Pre-chill your cooler and fill every gap.

Yes. The two biggest mistakes people make are tossing in room-temperature drinks and leaving empty air space. Fix those and your ice lasts twice as long.

Start with a cold cooler. Stick it in the fridge or freezer overnight if you can — an ice-cold cooler doesn’t waste energy melting ice just to cool itself down. Same goes for everything going in: drinks, food, water bottles. If you can put them in the fridge the night before, do it.

Use block ice. A big block melts slower than cubes because less surface area is exposed. Freeze a Tupperware of water or buy a bag of cubes and let them re-freeze in a block in your cooler the night before. If you must use cubes, dump them in but pour a little water over top to fuse them into one mass.

Pack it full. Air is the enemy. Every gap is warm air that speeds up melting. Fill voids with ice, cold water bottles, or even closed-cell foam. A full cooler stays cold much longer than a half-empty one.

Keep it in the shade, open it as little as possible, and don’t drain the meltwater until you’re done — cold water keeps things cold better than air does. A towel over the top adds a little extra insulation.

Your future self at hour 36 will thank you.