Well I'm not a canine nutritionist but I'll give my two cents if you would like.
Freeze-dried dog food if it can be fit into your budget. Its ultra-light, healthy, and customizable. There are many different companies out there these days that specialize in it so shop around.
I'm not a fan of dry kibble... but if that is what you're going with you can make it work. If the dog eats something other than its dog food, that is usually a clear sign that there is nothing physically wrong with him. So if he is turning his nose up at the offered meal -- Store it away until another meal time and don't give him something else, like jerky, until he has eaten his meal later. A dog will eat whatever is put in front of them when they become hungry enough. Much the same as a human thru-hiker's appetite, really. Just keep an eye on his health as you hike to make sure he isn't deteriorating.
Hope that was useful.