There is a Walmart in Cocoa Beach on Merritt Island - Rt 520, the West Cocoa Beach causeway, which I also heard referred to as Merritt Island Causeway, which runs west from A1A at about Ron Jons. Also a very large mall on Rt 520 on Merritt Island with usual stores and Berdines, a nice department store of the Federated chain.
I found that Berdines has a better swim suit and shorts selection than even Ron Jon's, and the prices were quite reasonable (especially with a big sale and additional 30% off )
Our college daughter arrived in Florida for our Dec. 14 cruise fresh from exams and with very little in the way of warm weather clothing (rather hurried packing- she did bring her formal so she could clean up nicely). We were able to completely outfit her the morning of the cruise with basics (shorts, sandals, nice shirts, etc.) at Berdine's with clothes that she actually liked. The selection was great.
At the same mall my husband got a formal shirt - to go with his tux - at a shop called Syd's. The shirt was under $25, and a 37 inch sleeve length. They had all types of men's formal wear there - a good last minute place.
I decided that in the future, I will put off any shopping until we arrive in Fl. and go to Berdines and other mall shops. The selection and prices are much better than at home, even in the summer.