If you need to finish a daily quest that requires you to eat a certain number of pre-war foods then you’ll want to consider hitting up these locations to gather some pre-war foods to keep in your stash.
The first place you’ll want to go to get some pre-war food would be the Watoga High School when the Monster Mash event is going on. This event if done right can provide a great number of candy (200+) which is considered as a pre-war food. Another place to consider would be the buildings around Whitesprings.
Although there isn’t as many pre-war foods provided like the Watoga High School location it’s still a great place to hit up. Here is a link to a useful map that provides various locations of pre-war foods aside from the ones listed above.