Freeze your water bottles

Freezing water bottles is the single best move for keeping a packed lunch safe on a long hike or beach day — they act as ice packs and give you cold drinking water as they melt.

The rule to know: perishable food is only safe for about 2 hours at room temperature, and just 1 hour if it’s 90°F or hotter. So the entire game is keeping cold food under 40°F until you eat it. A decent insulated lunch bag helps, but what actually does the work is putting frozen stuff next to the food. Two or three frozen water bottles buried in the middle of the bag will keep sandwiches, cheese, and even yogurt safe for a full afternoon.

Also, pick food that doesn’t need refrigeration in the first place. Peanut butter sandwiches, hard cheese, cured salami, nuts, dried fruit, whole apples, trail mix — all fine in the heat. Avoid anything creamy or mayo-based, soft deli meats, and raw chicken. If you bring something perishable, bury it between frozen bottles and keep the bag in the shade. Do not leave it in the car.

One more thing: wrap the bag in a towel or stuff it in the middle of your backpack where it’s insulated. And don’t keep opening it all day — every open lets the cold out.

Future you, at hour six, will appreciate it.