Wear whatever you're comfortable traveling in. You'll see EVERYTHING boarding the ship, from shorts and tshirts to ladies in floppy hats and dark glasses, full makeup and nails as long as their heels are high. You'll see couples dressed ALIKE... I don't know why, but some couples we saw on the Serenity this summer seemed to like matching outfits. It's true that Med cruises can be dressier, but not everyone follows that trend. If you're someone that likes to dress... go for it. If you prefer casual, that's fine. When we flew to Rome in July we purchased a transfer to the ship. We were put on a bus with 5 other couples. Those were the only people we boarded with. The only people that will think less of you for not dressing up will be the people dressed to kill. Personally, that doesn't bother me.