Make the ice pack the floor, not the wall.

The ice pack goes flat on the bottom of the lunch box, and everything else stacks on top of it.

Most people wedge the ice pack against the side or lay it on top of the food, and that wastes a ton of space. A flat ice pack on the bottom uses the full footprint and acts like a cold floor. Cold air sinks, so it still keeps everything cold from below — you’re not losing anything.

Stack your containers directly on top. Use square or rectangular containers; round ones leave dead corner space that you can’t use. Fill whatever gaps remain with soft stuff: applesauce pouches, string cheese, a cloth napkin. Those squeeze into spaces a hard container can’t.

You’re not giving up cold by putting the ice pack on the bottom — cold air sinks anyway.