When considering what to pack, bring one or two formal outfits (blazer and tie for him, cocktail dress for you)—ships typically have a "Captain's Night," where everyone is expected to dress up. But other than that, the bulk of your wardrobe should be smart casual for dining at night and during the day. For chilling on the pool deck? A swimsuit and cover-up will do just fine. On the whole though, some cruise lines are more formal than others, so read up on their website for the appropriate dress code.