Build a wrap or picnic plate
Combine tortillas or crackers with shelf-stable spreads, canned beans or fish opened at mealtime, and suitable fruit or vegetables. Choose combinations your group already enjoys. Read storage labels carefully: shelf-stable before opening does not mean shelf-stable afterwards.
Keep lunch flexible
A few small components are easier to adapt than a complicated recipe. Pack bread or wraps, a protein option, something crunchy and a piece of fruit. Perishable ingredients still need safe cold storage even when the meal itself needs no cooking.
Plan the cleanup when you plan the meal.
Make the backup meal complete
Put everything for one simple meal together, including a can opener if needed, clean utensils and a waste bag. Use portions your group can finish. Replace the backup after using it so the next trip has the same useful safety margin.