Another ration that hasn't been mentioned here yet and I feel deserves a mention is Survival Tabs http://www.survivaltabs.com/
While you could survive on these alone (though you would drop a bit of weight doing so), they are much better for you if used in supplement with other food. Foraging wild food, small stock of food in your pack etc. The theory behind them is pretty much anywhere you might need rations there will be some food to forage to supplement along with them. That you would not be surviving on the tabs alone but using them to maintain enough energy for a drastically reduced diet.
*edit to add, opps forgot to mention, one bottle, is claimed as 15 days of "food" That is a lot of ration in a small light weight package, plus the container can be repurposed as a water bottle. They even include a plastic bag inside the bottle so you can remove the tabs and use the container for water.
I have tried them and they are edible but not something you want to snack on if given the choice. Sort of a malty milky flavor. I have tested them both with just eating them alone and with foraging (eating small amounts of store bought veggies). Both ways helped keep my energy up and able to think clear and function well. I was able to work and do manual tasks without becoming overly tired. Though with a bit of veggies I was definitely happier, as the tabs don't fill you up and so you feel hungry more with no bulk in your tummy. So they seemed to me to work well for what they are meant for, a way to keep your energy up when you don't have much food.
While not as calorie packed as the other ration bars. Survival Tabs are supposed to be more efficiently utilised by the body, so more of the calories in them get used while most food you loose a large amount of the calories that was in the food.
survival tab wed site wrote:With most food products, 30 to 60 percent of the theoretical calorie content leaves the body unused. Survival Tabs are so completely digestible that 99% of their calorie content can be actually utilized for energy and 97% of the protein is actually available for repair or replacement of essential body substances such as blood, muscle, nerves, etc. Twelve Survival Tabs per day provide more than enough protein so sustain essential body tissues.
I don't know how this claim compares to other rations, or even how accurate it is. What I do know is I do have both Mainstay, and Survival Tabs in my INCH, along with "real" food. The Survival Tabs is a light small way to to add a lot more rations into a pack extending your available rations. For me I find them a great addition to my system, but would not want to rely on them alone. Worth checking out if your low on space and weight but need to get more food in your pack.