The best ice pack is a frozen water bottle.

A frozen water bottle is the only ice pack you need for an 8+ hour day on the trail. It keeps your food cold, then you drink it when it thaws. Two birds, zero extra weight.

The trick is to fill an old plastic bottle about 80% full (leave room for expansion), freeze it flat, and pack it at the top of your lunch bag. Everything below it stays cool. Don’t use your normal water bottle unless you’re okay losing that water to the first few hours of hiking. Use a dedicated bottle.

A few other things that actually matter: use an insulated bag, not a flimsy lunchbox. Freeze your food containers the night before if you can — a cold sandwich is a gift from heaven. And pack dense things (hard cheese, eggs, hummus) closer to the ice bottle, with bread and fruit on top. Open the bag as little as possible. That’s the real killer.

If it’s proper summer heat, add a small hand towel over the ice bottle. It slows down melt and doubles as a wipe. And skip the gimmicky gel packs — frozen water works better and doesn’t hurt to spill.

Keep it simple. Frozen water bottle, insulated bag, pre-chilled food. You’ll be fine.