Most sandwiches store better as components. Bread, wet vegetables and warm fillings change at different rates.
Store components separately
Cooked meat, sliced cheese, washed greens, pickles and bread usually keep their best texture in separate containers. Assemble close to eating time. This also makes it easier to reheat the filling without warming lettuce or soaking bread.
When an assembled sandwich can work
Simple deli sandwiches with moisture barriers may hold overnight. Peanut or seed butter sandwiches travel well because the filling is relatively stable, though jam can migrate into bread. Avoid storing sandwiches with ripe tomato, dressed greens or hot filling against bread.
Cooling cooked fillings
Refrigerate cooked food promptly in appropriate containers. Do not assemble a sandwich with steaming filling and immediately seal it; trapped condensation damages texture and may slow safe cooling.
Reheating
Remove fresh vegetables and cold sauces when possible. Reheat the filling or sandwich until appropriately hot, following official guidance for the specific food. A skillet or oven often restores bread better than a microwave, but the microwave is useful for heating the centre before crisping.
Use-by decisions
Follow package dates and storage directions. When in doubt about how long a perishable filling has been warm or refrigerated, discard it. Appearance and smell cannot identify every food-safety hazard.