I can't speak for specially manufactured products like MRE's, but I'm in the grocery business and can tell you this much. Canned prepared goods (spam, veggies, ravioli, ect) have on average 2 years shelf life with 6 months beyond the date. Frozen foods 18 months shelf with 3 months beyond the date. Some ultra pasteurized dairy products can have over a year shelf life unrefrigerated.
Perishables like bakery, meat, produce and dairy are just that, perishable.