Steak or chicken salad: pre-cook the meat and bring the vegetables and toppings. One topping that is so so yummy on steak or chicken salad - fried onion rings (you know the kind you use on green bean casserole at thanksgiving?) yumm
Un-fried chicken: you know, crusted but baked ahead of time so it's like fried chicken, but a tad healthier
I like cold pasta, so just the typical spaghetti and sauce would be good
Caprese Pasta salad: boil noodles, and toss with olive oil, balsamic vinegar, sundried tomatoes, fresh tomatoes, chopped fresh basil, mozzarella, roasted red peppers, olives, salt, and pepper.
Cold soups like gazpacho
If you think there's any possibility of finding a microwave (even at a 7-eleven/gas station) you can pre-make breakfast burritos and wrap them in sandwich paper (you can get it at Smart & Final) and then heat them up. They might even be good cold with some salsa.
Corn salad. I can't think off the top of my head how to make it, but it's really yummy and if you google it, I'm sure you'll find the recipe
I know you said sandwiches already, but here are some ideas for sandwiches:
chicken salad sandwich on croissants (just to be a little different): before you leave grind your chicken in a food processor with cashews, mayo and celery, add salt and pepper to taste & put in a tupperware (make sure it stays really cold in the cooler) then you can just spread it on the croissants.
Do like the English and make simple tomato & cheese sandwiches to eat with your cold gazpacho soup. They actually spread butter on the bread, then add a few slices of tomato and cheese - it's simple but good.
Make lasagna ahead of time. cold lasagna and a salad with bread is yummy.
Pizza.
Will you have access to a campfire? You can make Hobo Stew ahead of time and then just drop it into the fire to cook. Easy peasy:
get a big square of aluminum foil, in it place:
raw ground beef
raw cut up potatoes
corn
onions
garlic
other seasoning that sound good to you (I use worcesterhsire sauce and a little soy sauce and grill mate seasoning)
top with shredded cheese
seal aluminum by picking up corners and pinching together. Use a second piece of aluminum just to be sure. Put in freezer. When ready, toss the whole thing in the fire pit near the coals (make sure you have something to dig them out with) and leave them there for about 30 minutes. Remove carefully from fire, let them cool a bit, open aluminum, top with sour cream (optional but good) and eat directly out of the foil. This is our go to camping meal.
Chili and cornbread. and/or Frito boats.
That should get you started;)
Have fun!
Best,
S.