What ice-to-food ratio should I use for a 3-day cooler trip?

Use a 2:1 ice-to-food ratio by volume. For a 50-quart cooler, that’s about 33 quarts of ice—two 16-pound bags of bagged ice or homemade block ice bricks. Block ice lasts longer than cubes; freeze water in milk jugs. Pre-chill the cooler and food the night before. More ice is better.