I've thought about this as well. Since I generally loose 20 pounds on a hike I know that I have the stores there if needed. But is that optimal? I think there's a certain amount of morale building in being able to actually chew on something, at least for me.

My solution was simple and classic: Pemmican. Very calorie dense from all the fat. Provides a nice morale boost, something I think about more as my son gets older. and reasonably easy to store and carry. I just rotate it out when I make a new batch and haven't noticed any ill effects from 3 months in my pack.

Another nice advantage is that you can make it into whatever sized pieces you want. I've never messed with it since I always have a day pack with me but I think you could reasonably make small bars for a pocket kit.