Hi! We have been on two carnival cruises, I beleive there is only one formal night on a four day cruise, two on seven day. All the men in my family wear nice pants and a nice shirt on regular nights. On formal nights they wear anything from black pants and a tie or a tux if you want to spend the money to rent it. It really isn't the big problem that everyone thinks it is. You always wonder what to pack but I will tell you that you don't wear half of what you pack and it isn't worth taking up cabin space to bring it! On port days you wear your swimsuit and something over it! and then on at sea days you just wear something comfortable. You are on vacation so be comfortable and don't worry what the books say about dressing. they aren't really strict unless you wear shorts in the dining room at night. You will have a blast and if I keep going I could tell youwhat you should and shouldn't do all day long! Hope this helps! Have a nice day!