Good question. They are stable, long-shelf life foods, pre-cooked and, yep, ready to eat. A real, full-sized M.R.E. contains several components--including an entrée, side dish, dessert, cracker or bread, spread, drink powder, coffee, utensils, and accessories (including the much-sought after mini-hot sauce bottles).
They can be eaten cold and on the go, but I don't really recommend it. Chemical heater bags--just add water--are usually packaged with the MRE, and can heat them up in minutes, with some mess and chemical smell. You can also heat them in any way you can figure out--leaving them out in the sun, putting the foil packets in boiling water, etc.
MREs vs. Mountain House
I view MRE's as a compromise; Mountain House-style, freeze-dried backpacking meals are lighter, generally taste better, and have a better shelf life--Mountain House claims 25 years for their meals.
But, Mountain House meals require hydration--adding clean, drinkable water. You can't really just rip open the package and start eating, like with an MRE You can rehydrate the meals just fine with room temperature or cold water, but hot will obviously be preferred. There are flame less heater kits available to do this, or you can always just use any method for creating hot water.
Mountain House meals are typically much more expensive per calorie than M.R.E.s are. A full-MRE has in the ballpark of 1300-1500 calories and runs around $7 each. You'd have to spend twice that amount to get the equivalent calories in Mountain House meals.
Why would you want MREs?
If you anticipate a need for a stick to your guts, ready-to-eat, easy-to-heat meal and need it to last 3-5 years. Are they the ideal "bug out" food--no, not really--there isn't one. They are heavier than a freeze-dried meal, but they don't require the addition of potable water. If your bug out area is short on water, or if you can't store sufficient water supplies at home, that may be an important quality to you. Also, the fact that you can easily open one up and wolf it down while on the move is unique. Finally, their lower-cost may make them an attractive alternative to backpacking-style meals. They're a good option to add to your bug out bag.
Why wouldn't you want MREs?
If your plan is to bug in--stay put--then you'd be better served storing up conventional food storage--canned goods, rice, beans, wheat, etc. You'll get a lot more bang for your buck, and the qualities of an MRE (portability, no-prep) are a lot less important if you won't be on the move. You could consider storing a case or two, for barter, use on excursions or guard duty, etc.
How do they taste?
Most of the MREs I've ever sampled have been from passable to fairly good. Go in with very low expectations and you'll be pleasantly surprised. The quality is akin to mediocre cafeteria food--the kind of stuff you may have had slopped on your plate in elementary school. The military has done a lot to improve the taste of the latest MREs, and while you won't be craving them any time soon, they're perfectly edible.
How long to they last?
Many have heard stories of people eating 10-15 year old MREs and living to tell the tale. While these may be true, a safe rule of thumb to follow is 5 years when stored at room temperature. When stored in hotter areas (the trunk of your car over the summer), the shelf life is reduced. MREs often don't "go bad" at that point, and can still be eaten, but most of the nutritional value has broken down.
How do I tell how old they are?
MREs are all packaged with a four digit date code--the first number being the year they were made, and then the following three the day in that year. So 7235 would be the 235th day of 2007. When shopping for MREs, always look for this date, as it will tell you how old they really are. Many sellers will mention the "inspection date" instead, which is usually 3 years after the actual package date. So, someone selling MREs with an 2006 inspection date is selling 5-year old MREs--probably not a wise purchase, as they've probably exceeded their useful life.
What else to look for when buying MREs?
Sellers will often push MRE components--usually the entrées--as full meals. This is not a full MRE, which should be large pouch and contain several different components (entrée, side, dessert, bread, etc.). It is generally not approved to sell the real-deal MREs, though they are available on eBay, and at gun shows and army surplus stores. These come in an unmistakable brown pouch.
There are also various civilian suppliers that put together the same MRE components to provide a similar--but not quite the same--product. Make sure to review the content list on non-military MREs before purchasing so you know what you're getting. Some will leave out the flameless heater or provide substandard crackers, desserts or accessories. A dead give-away is that they will not be packaged in the same brown pouch as real military MREs.
- MRE packaging is generally overly bulky--lots of bags and boxes. You can cut down on weight and space by opening them, field stripping them down to what you want and losing the rest.
- MRE cheese and peanut butter spreads are very good, and make good snacks along with crackers. Keep a few stashed in your desk/car, along with a package of Ritz crackers, for a good snack.
- The MRE chemical heaters release hydrogen gas as they work. Placing an activated heater inside a plastic bottle and sealing it up can produce explosive results. I don't recommend attempting it, but something to file away in the memory banks.
- The military is releasing a new kind of MRE--First Strike Rations. These are lighter, more compact, and designed to be eaten by hand, on the go. The entrées take the form of sandwich pockets.
- Along with First Strike Rations, expect some old MRE components to be rotated out and new items in. Chipotle snack bread, salsa verde, and Twizzler Nibs are among the items to be added.