i've learned never bring dress up clothes unless i know i'm going out for a nice dinner or on a cruise...then you definitely have to pack some nicer things with another pair of shoes! most of the time, you can still wear your jeans anywhere restaurant wise (at least overseas we haven't had much trouble) but i do wear nicer clothes as my non-rev attire (esp since you have to) and sometimes use that as my nicer outfit just to pack even lighter!
but, i agree with roz, dressing by color code is pretty much essential if you care about your appearance while on vaca!
oh yea and always take a bathing suit! you just never know when you'll have a nice quiet pool to rest your toesy's in...