Although the John Updike short story "A & P" at first appears to be told in the present, the whole story serves as a kind of flashback. We know this because Sammy tells us
Now here comes the sad part of the story, at least my family says it's sad but I don't think it's sad myself.
Sammy narrates the story in retrospect, since it is apparent that his family already knows about him quitting his job, and they are "sad" about his decision. Updike's foreshadowing is subtle. One hint comes in the "sad part of the story" quote mentioned above. The reader can also assume that eventually something will be said about the girls' underdressed attire, not exactly appropriate for the store that is patronized primarily by old "cash-register-watchers" and "sheep."
You know, it's one thing to have a girl in a bathing suit down on the beach... and another thing in the cool of the A & P...
A final bit of foreshadowing comes when Sammy says that "everybody's luck begins to run out." His own jobless future is predicted in the final sentence, when
... my stomach kind of fell as I felt how hard the world was going to be to me hereafter.