pharmacy tech wanna be said: still need your help
Assuming that your first interview was with someone at the Store MGT or DM level, the second interview is only a screening to see if you are going to be a good team member.
The first interview proved that you were the most proficient applicant they had. The second interview is at a direct management level so they can assess whether you mesh with your teammates for 8 hours a day 40 hours a week.
My advice. Do whatever you did in the first interview: It worked before! Be yourself; friendly, capable, and ready to hit the ground running. I would also bring in your ID and your eligibility to work document (SS Card or Birth Certificate) this shows you are confident that the job is yours and allows them to take the next steps in the employment process....