You can “reasonably stockpile” years worth. If part of your stockpile is ammunition and seeds, you can have enough to feed your family forever. Literally.
Nothing short of nuclear war or invasion will make any societal collapse a “forever” event.
I’m not so sure about that.
If we lost the electric grid for say 60 days, then most, if not all of it might be down forever.
And millions would probably die. You can’t just turn the clock back two centuries and expect anything else.