Freeze a water bottle instead

Freeze a water bottle the night before and throw it in your lunch bag — it works as well as any ice pack, and you get a cold drink out of it by the afternoon.

Fill a bottle about 80% full so it doesn’t burst in the freezer, then tuck it next to your food before you leave. Water holds cold longer than most gel packs do, so it tends to outlast the store-bought kind. When it melts, it’s just water.

If you mean no cold source at all, that’s a different problem. Your options become foods that are safe at room temperature: peanut butter sandwiches, nuts, dried fruit, whole fruit, crackers, hard cheese, shelf-stable tuna packets. Perishable stuff — chicken, eggs, mayo, deli meat — should not sit out all day. The four-hour rule is real, and food poisoning is not a fun way to spend a trip.

Whatever you do, start everything cold. Pre-chill the bag itself, freeze the yogurt or grapes that go in, and keep the bag in the shade instead of on a sunny car seat. An insulated bag only slows warming down; it can’t actually cool anything.

A frozen bottle of water is the answer — even if your lunch is fine at room temp, it’s still a nice cold drink.