@Kels_316 Dehydrated is the go for dinner. The easy and $$$ answer is Back Country or similar brand. as a 15yo he is probably going to need the large size or suplement a small serve with something like 2 min noodles or pre-cooked and then dehydrated rice or pasta. (rehydrating pre-cooked rice or pasta takes a fraction of the time and water that cooking it from the packet does)

I have the luxury of time and a dehydrator so I make my own. This sort of stuff: https://slowerhiking.com/recipes

You can dehydrate in an oven but it's still a bit fidly: https://eatsleepwild.com/can-you-dehydrate-food-in-an-oven/

You can reinforce 2 min noodles by adding dehydrated veg, spices, and that rubbery Jack Links jerky. it rehydrates into meaty chunks that are arguably better than the original product. Adding a piece of Golden Curry block will jazz it up as well but maybe a bit too much mucking around for a 15yo.

Single serving foil packs of tuna or salmon are good protien to weight ratio, add to dinner or eat for lunch.

If you're not dehydrating your own frozen veg then supermarket options are pretty much limited to peas and mushrooms. Instant mash potato has little value but it does fill you up. Really need to prepare it seperately though IMO.

Carrying something heavier like a ready made curry in a foil pack is fine for the first night. Its not usually a long day and you shed the weight early. Also hard boiled eggs for breakfast or lunch the next day. Over 5 days hard cheese or the drier salamis are fine too, despite what the pack says.

On other meals, Oats are the best breakfast, either in muesli or instant oats for porridge. Single serve sachets aren't normally big enough. I pre mix a serve with powdered milk in a snap lock bag so I can just ad water and leave it wrapped in insulation for 8 or so minutes to eat warm. Can add sultanas too. single serve sugar for sweetening or honey if you can get them.

I always eat lunch cold, it's really just an extension of my snacks. I pack my lunch portion seperate to my snacks so I don't eat it too early. I eat the most fried, salty or sweet crackers you can get. Also those Mini Wraps will last for days. Dried fruit and nuts in moderation but I get sick of those quick and crave more fast calories. Sugared nuts, trail mix, soy crisps. Belvita biscuits are good anytime from breakfast to lunch. Dry, hard jerky is good to conserve food if there is a danger of eating out of boredom. If everyone else is cooking for lunch throw in some 2 min noodles.

For beverages I use a coffee bag for 2 brews in the morning and a teabag at the end of the day. I use powdered milk as a whitener. Chocolate drinking powder sachets is also good. I carry 2 of the heavier Cup-a-Soups per day. One I have before dinner and one just before bed. They can be a good hot snack at lunch too.

You can add hot water to cous cous, a cup-a-soup (and any dehyde veges), stir and let it sit covered to make an ok easy dehyde meal but getting the water right takes a bit of practice.

I also find pre-sorting each days food and beverages and bagging seperately helps.