Soggy bread is a layering problem.

The trick is to keep the moisture from ever reaching the bread, not to fix it after.

Your best tool is a waterproof barrier between the wet stuff and the bread. Butter, mayo, or a cheese slice all work. Even a dry lettuce leaf will do the job—it takes the hit so your bread doesn’t.

The second move is to dry out your fillings before they go in. Pat tomato slices dry with a paper towel. Salt sliced cucumber and let it sit for a few minutes, then pat it dry. It sounds fussy, but it takes thirty seconds and removes a surprising amount of water.

And don’t forget the geometry. Put the wet ingredients in the middle of the sandwich, between dry layers like cheese or meat, rather than pressed against the bread. If you’re packing a container lunch, the bulletproof move is to pack the wet stuff separately and assemble at lunch—but the barrier trick gets you most of the way.

Assembling at lunch is the only perfect fix, but a good barrier is 90% of the game.