Spam! As long as the can isn't compromised it should last forever!
FWIW, I have opened and eaten small quantities of "expired" MRE's (mid 80's vintage) as late as last year with no ill effects. Some of the stuff was a little stale but edible. Temp has a great effect on storage life, colder is better. In theory at least, an MRE in the fridge should last 30 years or more, in your car trunk with 95 degree summer heat, a month or three. As long as the pouch is intact, no swelling from gas, and no bad smells/tastes (beyond the "normal" mre tastes!) it should be safe to eat. My Marine friend says the C-rats he was fed in Vietnam were 1940's WWII surplus stuff. Other than the cigarettes falling apart they were in good shape. Yes, the dreaded Ham and Lima beans were still disposed of by means other than eating!