I've been using Sainsbury's own mashed potato for years as a trekking food. It comes in a box of five two portion foil envelopes which have to be mixed with half a litre of boiling water to be re-constituted. Simple! I add sliced dried sausage, parmesan, tuna, bully beef herbs etc (but not all together!
Couscous is another favourite as it,too, only needs boiling water to be re-constituted. Additions as above with herbs,etc.
Ramen noodles were another standby.
What do the above have in common? They are light, simple to fix at the end of a long day and require little fuel to cook. They can be made in a "pour and store" or similar pouch using one boil up of water the rest of which is used for your brew.
I usually carry a small vial of mixed salt, pepper, garlic powder and dried herbs to spice up the above. Curry powder and mixed spices are also possibilities.