In 2007 we did a Chistmas cruise on Carnival, which is a pretty informal cruise line in general. Their formal night is "Black-Tie optional", which means a dark suit is OK for gentlemen, so I just wore my Argyll and waistcoat with a white shirt and a tie, and was more 'dressed up' than many passengers at the dinner. Except for the tie and white shirt I got more than one use out of the rest of that outfit during the 5 days we were on the boat, so I did not need more than one case to bring along my kit. I took 3 kilts with a few co-ordinating shirts and hose etc. and only one pair of jeans that I wore once for our horseback riding shore excursion.