I'd pull out the stove and boil some water.
Maybe you can give it a try at home but maybe he will like Idahoan Potatoes.
Just add water. Or maybe some soup. Just add water.
Here's the potatoes we eat frequently:
http://www.idahoan.com/Safeway sells Black Bean soup that we also eat for lunch frequently.
Tuna in a packet is also a staple for me backpacking.
I usually take along some type of hot sauce (like Del Taco's Del Scorcho).
So definitely yes on the Tuna.
Good luck