Frozen water bottles are the best lunch box ice packs

Frozen water bottles keep a lunch box cold just as well as store-bought freezer packs, and you get a cold drink at lunch. It’s the same trick, minus the plastic goo inside.

Here’s why it works: a full bottle of frozen water is a big block of thermal mass. It takes hours to thaw, and while it thaws it absorbs heat and keeps everything around it below the danger zone. Freeze it three-quarters full so the ice has room to expand, and wrap it in a cloth or paper towel so condensation doesn’t sog your sandwich.

Frozen fruit works too — grapes, berries, even a frozen yogurt cup. It won’t hold the cold as long as a giant water bottle, but it’s plenty for a short morning and it doubles as dessert. Whichever you use, put the cold thing on top of the food, not under it. Cold air sinks, so it’ll circulate downward and cool everything more evenly.

Don’t overlook the basics either: an insulated lunch bag beats a paper sack by a mile, and if you can toss the whole packed lunch in the fridge for ten minutes before you leave, you’re starting way ahead. No freezer pack required.

Future You gets a cold sandwich and a cold drink — that’s a two-for-one.