http://www.mreinfo.com/us/mre/mre-shelf-life.html

My favorite reference site for MREs smile

Rule of thumb: if the outer package is not "bloated" it's generally OK to eat smile
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Member of the toughest, meanest, deadliest, most unrelenting -- and ablest -- form of life in this section of space, a critter that can be killed but can't be tamed. --Robert A. Heinlein