A bleach rinse makes it good as new

Sanitizing a second-hand lunch box is easy: wash it with hot soapy water, then wipe it down with a food-safe bleach solution and rinse.

The soap handles the grime, but soap alone doesn’t kill everything. If the box came from a stranger, assume there are germs you can’t see. A bleach solution of about 1 tablespoon per gallon of water is food-safe and kills almost anything. Wipe every surface, let it sit for a minute, then rinse thoroughly with plain water and air dry. That’s it.

If it’s a fabric or insulated bag, skip the bleach. Run the whole thing through the washing machine on hot, or if it’s not machine-washable, wipe it down with a vinegar solution and let it dry completely. The key is letting it fully dry before you store anything in it—moisture is what lets bacteria come back.

Don’t overthink it. One good scrub, one good rinse, and that box is yours.