17 year-old MRE tuna surprise will make your mouth pucker but probably won’t kill you.
I got a case of USAF survival rations that are in a spam can that is airtight. They were packaged around 1975 and I open one about every two years and they suck just like they did when they were a year old and are still wholesome (note I said wholesome, not edible).
[17 year-old MRE tuna surprise]
Yankee Bean Soup, cole slaw, and Tuna Suprise
https://www.youtube.com/watch?v=_AOeSrLCD-U