If you can set aside issues of flavor for a moment, consider combining starches, fats, and sugars in the highest densities possible and then using protein bars for protein. This could be dry potato flakes mixed with olive oil, for example, and hydrated with a bit of water. You could also try something like bringing cake or brownie mix, adding oil and water, and then just eating it with a spoon, that is of course unless you want to try to 'bake' it in a pan over a fire or something creative like that. Quick-cook oatmeal is also dense complex carbs and rehydrates easily, even without heat. Add trail mix to it or some other combination of nuts and dried fruit and/or other sugary garnish and add coconut oil to make it creamy and add very high-density fat calories. These may not sound like the tastiest meals but if you're trying to pack a lot of calories with little weight and you're filtering water along the way, they'll work. Most importantly, experiment with ratios of complex carbs, fats, and sugar that works for you. I once tried living on mainly nuts and sunflower seeds as these have lots of calories and protein, but I found that I just can't get the energy from fats that I can from complex carbs. This may be different for people depending on the ability of their livers to break down fats into simpler carbohydrates, though, idk.