Skip rigid bento boxes — get a collapsible container

The best slim and foldable lunch box for a small backpack or tote is a collapsible container that flattens when empty, like the Black+Blum Folding Lunchbox.

Rigid bento boxes are great, but they eat up space in small bags and can’t flex around other stuff. A collapsible box solves that: it goes flat when empty, so you can slip it into a gap or just leave it in your bag without taking up valuable room.

There are two kinds: silicone/soft-sided containers that squish, and folding boxes with hard panels and a hinge. Silicone ones are better for soft foods and easy cleanup; folding boxes keep their shape better and protect contents. For a small bag, pick one that folds flat rather than just squishes, because it’s easier to slide between books or a laptop.

Check the expanded capacity. Many are around 0.6–1L, which is enough for a sandwich plus a snack. Also look for a leak-proof lid, or bring a separate bag for wet stuff like fruit. If you don’t need a hard box, a reusable silicone food bag (like Stasher) is even slimmer, but it doesn’t offer much protection. For most people, a folding box is the sweet spot.

Your back will thank you when you’re not carrying a lunch box brick all day.