In the wasteland you encounter stuff like Pork 'n Beans, Fancy Lad Snack Cakes, etc. But how did all that food survive in an edible state for 200 years? Mabye the canned food, but what about the food you find in boxes? Pre-war chemical technology?

It's never stated, I think we're just supposed to accept it apparently. In the old Fallouts you could find some pre-war food but not of it was edible.

Fallout Sciece! I just hope the next Fallout moves away from it. To make pre-war food rare and if we do see it we hear wastelanders saying "I can't believe you are eating that crap."

It shouldn't have, but it does.

I believe the idea for it is based off the feeling during the 1950s that pervaded following the introduction of ready-to-eat vacuum packed dinners and the like. The notion being that they could "last forever" thanks to handy-dandy science.

In the Fallout Universe, that, along with much of the fantasies from the 1950s, becomes a reality.