The Mainstay type rations certainly have their place, but I prefer something a little more varied. The storage longevity is mainly due to the mylar vacuum sealed packaging, but this can be replicated at home with a vacuum sealer.
Typically I would vacuum seal the contents shown below (but these items have been pulled from my day pack food baggy)
Although some water is required for the above contents (around 160ml for the Cous Cous and another 300-600ml for a couple of cups of tea) in terms of water usage would compare favorably with a US MRE in terms of water use. I doubt there is such a thing as non thirst provoking food unless it was possibly canned fruit etc.
In terms of weight v Calorie performance the above meal provides around 1600 Kcal for a 420 gram weight. Typical cost for this meal using the supermarket goodies is around $4-4.50, so would be around 100gms heavier than the 4 Mayday 400 Kcal bars.
Edit - Actually the simmer soup requires 600 ml of water according to the instructions so if water was limited then the 212 Kcal contribution would have to left until enough water was available. (but that is not really a problem here in Scotland)