Avocado, can be eaten with a spoon
Great minds - I'd actually thought of that just after starting this thread. I figured that the calories-per-gram are about the same for eggs, those tuna meals, and avocados. Avocados are like eggs - come in their own shell and survive for a while in heat! I could even fill them with those tuna things. Or poached eggs. Oh, the possibilities.
I think I'll be changing my backpacking food approach as a result of this thread! Normally it's cold food and water, and even tea is a luxury. I do have a very nice non-stick Trangia stove though, which I normally only use when car-camping. I'm tempted to lug it around the hills so I can go full-on Keith Floyd now, though!