It depends on what it is. Some things, like dried macaroni or oatmeal would probably be alright, but other things that are more perishable, like opened jelly or cheese would not.
Popcorn would most likely be OK to eat after the expiration date, but it also would most likely be starting to get stale and soft. Ik!
yes, as long as it has been in the freezer and you just took it out.
it isn't smart but its your health
Of course...it's just a "best if used by" date. If it smells bad, throw it out. Otherwise, enjoy!