OK, this one's a tad obvious. This story is all about clothing. Whereas the drab attire of the standard A&P shopper characterizes her as a spiritless housewife, the bathing suits worn by the girls characterize them as fresh and exciting. This is, of course, if we follow Sammy's point of view. From the point of view of Lengel, the manager, this clothing choice characterizes the girls as indecent or improper.
Sammy's A&P apron and bow tie at first characterize him as something of a follower, like the people he criticizes. To keep his job, he too must follow the A&P dress code, which for an employee includes an apron and a bowtie. When he quits, he removes these items, leaving the store in "the white shirt that [his] mother had ironed the night before" (30).