brad - FYI Carnival is probably the most casual of the mainstream cruise lines, with that being said for daytime wear shorts with a polo or golf shirt will be perfect, a nice plain cotton t-shirt would also work very well, for casual evening wear, dockers type pants with the golf, hawaiian or polo shirts will be perfect. You could probably get away with out a sportsjacket, but if you want to wear it then go for it, you would only need one. As for quantity i plan for my DH two days on a pair of shorts, fresh shirt daily, same for casual pants, two evenings on a pair of pants with a fresh shirt each evening. 1 pair of swim trunks, good walking sneakers, water sandals, 1 pair casual shoes, 1 pair dress shoes.
Fabrics - go with natural fabrics, cotton, linen, silk, summer weigh wools.
hope this helps.