The most important thing is something easy to cook! It's amazing how a long days walking can reduce teenagers ability to think logically so easy meals that can just be reheated or made up with boiling water in a single pan are great! All the things you've already got sound great!
Other evening meal item suggestions:
Instant mashed potatoes (can be made up with just boiling water and has a really high carb to weight ratio)
Those packet pasta meals that you can make up with water or cup a soups
Pot noodles can be emptied into ziplock bags and made up in a mug to reduce bulk, just use the plastic bag to cover the top of the mug in the place of the lid while cooking
Meat items such as matterson sausages, tinned tuna and other precooked items that only need reheating are a much better choice than raw
Portion size and calorie wise most kids will eat about double what they normally would so make sure to pack plenty!
Snack/lunch ideas:
Nutella and peanut butter are calorie dense and okay out of the fridge so good for day 2 sandwich fillings
Beef jerky, pepperoni and other high protein snacks are good for energy
Also baby bells and other individually packaged cheeses are quite popular
Breakfast bars
Dried fruit (I generally wouldn't recommend fresh as it takes up a lot of space and normally isn't eaten!)
Obviously some sweet treats as well!
When packing food separate into ziplock bags for each day and put snacks for later days in the main compartment of the bag (more difficult to get out!) Which helps to keep it all from being eaten on the first day! Each morning before walking that days snacks can be moved up to a top/side pocket
Try to alternate between snacks containing mostly fats, proteins and carbs eg some cheese for snack one, beef jerky for snack two and then a cereal bar for snack three to get the best energy distribution, although most kids will eat all their chocolate on the first morning!
If they like hot drinks then the little milk and sugar sachets you find in cafes are ideal
I also would recommend an "emergency" bar of chocolate, not for actual emergencies but for when you're tired and wet and a bit lost and they need that little pick me up!
One of the best pieces of advice that I can give for while they're doing it is if you ever get to a point where everyone is miserable, snappy and can't agree what to do next the best way to solve the problem is probably all to have something to eat and then reassess!