Get a dry bag, not a lunch box.

For bike commuting, the best lunch box is a waterproof dry bag with a rigid insert — it keeps food dry, contained, and un-smooshed.

Regular lunch boxes fail on bikes in two ways: zippers leak after a season of rain, and soft sides don’t protect a sandwich from your pump or laptop. A roll-top dry bag solves both. It’s actually waterproof, and since it packs like a cylinder, it fits neatly alongside the rest of your gear.

Most dry bags aren’t insulated, but that’s usually fine. Your commute is a few hours, not a camping trip. Need cold food? Throw in an ice pack. Need hot food? Use a thermos inside the bag. For structure, a plastic lunch container or a small cutting board in the bottom keeps things from getting crushed.

If you want something ready-made, the Yeti Daytrip is solid, and Ortlieb makes proper roll-top panniers that double as lunch carriers. But honestly, a 10-liter dry bag and your normal containers is cheaper and just as reliable. Your lunch shouldn’t be the thing that gets ruined by a puddle.