I think that in canon, most food in the Fallout world has been loaded with preservatives, which allows them to survive much longer than traditional canned food.

From what I've been told by the F1/2 devs any prewar food was a anomaly (and I've spoken to some of them at length on mail groups and IRC), I know a lot of newer players don't like it but they based a lot of F1/2 on genera films from that era and the understanding of nuclear war at that time, while it had a lot of style elements from the 50's it wasn't the 50's in the 2070's, it just borrowed the styling in parts (just to add to this, Im 35 and I dress and talk like a Victorian, it started as a thing for my restoration business but it over timed became me, and I have no desire to become modern) but that is a choice in a period of time I can do such a thing, however if there was a nuclear was today right this moment I'd likely have enough skills to survive, if not thrive when it comes to farming and associatedly useful skills (you know that nice shovel you have? Yea when it's used regularly it doest last,you end up needing someone who can make spades from wood OR a blacksmith, and cutting a spade shape out of wood isn't right or beating or cutting a shape out of mild steel isn't the same).

After all that we get into food preservation, this is a skill we dont pay attention to in the modern westernworld, oddly if one thing helped our growth was learning how to support a preserved meat industry on a large scale, and we also learned from rediscoverd texts of pre Christian (monotheism is a curse) farmers about crop rotation, oddly its something we have forgotten again because of hyper modern monocropping thats killing the soil.