Use a 2:1 ice-to-food ratio.

That’s two parts ice for every one part food, by volume. For a 50-quart cooler, that means roughly 33 quarts of ice—about two 16-pound bags of bagged ice, or better yet, a couple of block ice bricks you freeze yourself.

Why so much? Because a 50-quart cooler isn’t massive, and on a 3-day trip you’re opening and closing it multiple times a day. Every time you open it, cold air escapes and warm air rushes in. The ice takes the hit. If you skimp, you’ll be eating warm sandwiches by day two.

Block ice lasts longer than cubes. Fill empty milk jugs with water and freeze them solid. They melt slower and double as drinking water later. Cubes melt fast and leave you with a soggy mess.

Also: pre-chill your cooler and food the night before. Don’t put warm drinks in expecting ice to cool them down—that’s throwing ice away.

You can’t have too much ice on a 3-day trip. More is better.