Peanut butter: the oil will go rancid.I might eat yogurt at a week over. Really depends on what it is.
Milk is the smell test. The dates are "SELL" by not "use by". As mentioned, how cold is it kept getting it home?
Cheese: I cut off the mold and keep eating.
Does peanut butter ever go bad? We dont refrigerate ours... should we? It looks kinda oily sometimes, but never seems to mold or go bad? Is it self resistant to degradation or something?