My husband takes, depending on the cruise length, 1 or 2 dress shirts to wear with his suit for formal nights and then changes into another shirt after dinner. He still wears a nice shirt but not his white ones.
We have done a couple of 14 day cruises with a couple of nights pre-stay and a week post stay with temps ranging form the 50's to the 90's during the day so we needed two seasons of clothes. We do pack 2 bags each plus our carryon. We have not had to do laundry on board the ship yet.
This year, we will probably need to have our clothes laundered/cleaned as we will be doing a 28 day cruise with a couple of days before and a week after. Once again, we will need to pack for two seasons as temps during the day can range from the 50's to the 90's.