Butter the bread

The fix is a moisture barrier: spread a thin layer of fat — butter, mayo, or cream cheese — right to the edges of both slices of bread. It seals the bread from tomato juice and everything else wet. Bread is a sponge; fat is waterproof.

For extra insurance, keep the wettest stuff out of the sandwich entirely. Pack tomato slices, pickles, or sauce in a small tub and assemble at lunch. Cucumber and tomato are the worst offenders — they sweat water even when they look perfectly dry.

Two more small things: don’t pack the sandwich while it’s still warm (steam turns into soggy bread), and throw a folded paper towel in the lunch box to soak up condensation. If you’re prepping the night before, use sturdy bread — sourdough, ciabatta, a decent whole grain — and toast it lightly. Soft white bread is a lost cause by hour five no matter what you do.

A soggy sandwich is a sad lunch, and the fix costs about twenty seconds.