Pack lunch vertically against the back panel

The fix is to pack the lunch box upright against the back of the pack, not flat on top of your books.

The problem is the flat position. A lunch box lying flat in the bottom of a backpack becomes a hockey puck. It slides and spins with every step. Stand it upright against the back panel and your back pins it in place. The rest of your gear pushes it against the panel and it can’t go anywhere.

If your backpack has a padded laptop sleeve, that’s the VIP parking. Most lunch boxes slide right in there and you get a bonus layer of crush protection for free.

Also: fill the empty space. An underpacked bag is a loose bag. Stuff a jacket or sweater in next to the lunchbox. Bags that are packed full don’t shift, and things that don’t shift don’t crush anything.

If food is still getting demolished, the container is the weak link. Soft insulated bags fold like origami under pressure. A hard-sided bento box shrugs it off.

Your sandwich will survive. That’s the whole game.