A wet rag is the only tool you need

The way to keep a wooden lunch box from warping or cracking is to clean it with a barely damp cloth and dry it immediately. The trick is never letting it get soaked in the first place.

Wood swells when it gets wet, then shrinks as it dries. If that happens unevenly, you get warping. Cracks come later when the wood dries out too much. So skip the sink bath, the dishwasher, and the soaking. A quick wipe with warm water and a drop of dish soap on a damp cloth is all it needs. Dry it with a towel right after, and leave the lid open overnight to let any moisture escape.

Once a month or so, rub in a little food-safe mineral oil or beeswax. That’s the real crack prevention — oil keeps the wood from getting brittle. And don’t let wet food or fruit sit in there for hours. That’s where the damage actually starts.

Think of it like a cutting board — wipe, dry, oil, and the thing will outlast you.