Canadian IMPs are far superior to American MREs. Some thoughts on them.
ShadowChaser mentioned they are waterless/do not require water. Yes and no on both. Every main meal and dessert I have come across have been packed in sauce or syrup. So there is fluid in them (and this is part of the weight). There are components -instant potatoes and pudding and drink mixes- that do require water. The brade is very dry and might benefit from dunking in soup.
Re: expiry dates: The Canadian IMPs come in brown bags (almost like a lunch bag) with the year printed on them (06, 07, 08, etc.). Official line is 3 years from the year stamped. I have eaten all components from 5 to 6 year old IMPs with no ill effects. There are off-the-shelf candy bars and M&Ms packed in them and they are often well past their expiry dates. No problem. I'll put it this way - I had an 07 meal with Star Wars Epsiode II M&Ms in them
Gulagger mentioned them not being that great. Having served in the reserves, many of our exercises were catered. Given the choice between the catered meals and the field rations, we'd take the field rations any time.
As for calories count, each meal (if you eat EVERYTHING) contains rougly 1200 calories. I know people who have survied for 50+ days on these (though not always 3 times a day). They do have a tendency to clog the body's drains though. In terms of nutrition, they are apparently far superior to most countries rations.
The best part though is that no part requires cooking. most of the IMPS I've eaten I have eaten cold. There are some, however, that I would not even touch if they weren't heated.
If anyone wants any I do have a small stash of bread available! :P
As a side note, if you go to London Drugs and purchase a "Kitchens of India" instant curry, they are packaged and prepared the same way as the main course of an IMP.