As I sit here, in Iraq once again, I count myself lucky not to be eating MREs - "Meals, Ready to Eat", or as some of us in the U.S. Military call them, "Meals Refusing to Exit." The reason for this is the constipation that MRE consumption usually causes.
One of the first experiences a Marine recruit has with an MRE is the field-strip. Taking each item out of the tan, heavy plastic wrapping, throwing out all the crap you don't need (eg. candy, cakes, flameless heater, basically anything enjoyable, or that may make it more edible), and packing the rest into a pocket of your ALICE pack. This brings the size of the meal down from roughly two inches by six inches by twelve inches to about an inch by three inches by five inches. This can vary by the meal and by what you keep and don't keep, of course. Keeping everything that comes in the package except for the package itself can still save quite a bit of room. Stick the candy and cake in a pocket for munching on the move, and put the rest in the pack.
There are twenty-four seperate MREs, and they're changing with the times. They come in two cases - Menu A and Menu B. Each 'menu' consists of twelve different MREs - one through twelve for "A", and thirteen through twenty-four for "B". Each MRE comes with a main meal, which is what the MRE is named after. Some also come with a side dish, which may be anything from mashed potatoes (decent), to the rice pilaf (nasty, IMO). If it doesn't come with a side dish, it usually comes with a fruit of some sort. Also included is usually either a combonation of A) Crackers with peanut butter, B) Vegetable crackers with cheese, or C) Wheat bread with some sort of fruit preserve. Each one has candy of some sort (Don't eat the Charms!), as well as some sort of beverage base - either tea, cider, or a sort of a Kool-Aid/Gatorade powder. Also included is a condiment package, with salt, pepper, water-resistant matches, and a spoon. Finally, and for some meals, most importantly, there is a flameless ration heater.
The flameless ration heater is a boon to anyone who has the time and patience to use it. It consists of a packet of some sort of substance, enclosed in a sort of filter paper which heats up enough to cook the meal inside the package in which it is inserted. The packet comes inside a plastic wrapper which is barely large enough to hold a meal from an MRE. This diagram below is almost a quote from the package - except that it's from memory:
v-- MRE box
------ OO (-- Rock or something
Yes, it actually says, "Rock or something." At any rate, each main meal comes inside a lightweight cardboard box. Take the meal out of the box, slip it down into the heater, pour water into the heater up to the fill line (They -try- to make it idiot-proof. It doesn't work), then you fold over the top of the plastic package (you didn't tear it off too low, did you?), placing the entire thing into the cardboard box, with the folded flap facing up, and on the upwards slope. After roughly five to ten minutes, the meal will be steaming hot, and ready to eat. Of course, if you don't have time to use the heater, you can still eat the meal without cooking - it's already pre-cooked. Be warned, though, that some of it tastes like crap if you don't cook it.
Now for the eating part. The packages the meals come in are plastic-reinforced foil, vacuum-packed. It comes with indentations, similar to those you'd see on a single-serve package of beef jerky or something. Unfortunately, the effect of using these tends to be similar to uncontrolled opening of a bag of potato chips, if you're not careful. Use a knife on it. Another point to make is that these indentations are aligned such that you eat the meal with it held vertically - similar to the effect of a sixteen-ounce cup smashed flat. The spoon isn't quite that long, and this usually results in very messy fingers, depending on the meal. If the moist towelette inside the condiment packet doesn't clean it up... well, you've got a long time before you can wash your hands again if you're eating MREs in the first place. Someone used to eating MREs will open the package horizontally instead, which allows for much cleaner eating. Incidentally, since there's no way to tear it this way, that's why you've got the knife.
One of the disadvantages to not keeping the outer wrapping bag is disposal of the waste. You don't want a runny beefsteak with mushrooms wrapper getting all over your pocket, and you can't just throw it at the roadside, even out in Iraq. Keep the bag - it doesn't take up that much more space once you have everything out of it, and it's worth it to keep yourself from being a mess.
As of this time, I haven't been able to find a listing of all the MREs available at this time - seems that nobody sells the cases we're currently using. I'll keep on looking for the list, but trust me - you don't want to know anyway. Most of the meals really suck.