You can buy pre-cooked chicken, turkey, and tuna in foil pouches (less weight than cans) that need no refrigeration. Look for items that require minimal cooking in the rice and pasta aisle of the grocery store. There are a lot of noodle or rice side dishes that require only adding boiling water and letting sit, or minimal simmering. You can add a pouch of precooked meat to them while the sit or simmer and have a filling one-pot meal with little preparation time.

Instant mashed potatoes are another good option. You can get them in different flavors in cyclist-sized single serving envelopes (2-3 normal person servings!). All they require is adding boiling water, stir to mix and let sit for a few minutes.

Summer sausage is another option for meat that does not require refrigeration. If you can find it in small single meal sizes, you can eat it with some cheese and crackers. It can make a nice easy lunch.

Pita bread (or flour tortillas) pack easily and with some good old peanut butter and jelly makes for a quick filling lunch.

Of course fresh fruits and vegetables are always a good idea especially if there is a grocery near your campsite.

Try to keep things simple. When you're tired, it's hard to do much cooking.