Gosh, that really is a pickle. You already spent far more than the usual wedding but you did get a lovely vacation from it.
I think memories are far more valuable than mere cash or even gifts (not all gifts are useful right?). Perhaps I could suggest making a lovely scrapbook filled with pictures of the cruise and all the happiness you all shared. You can include your parents in on this and share the gift. This will explain also why this gift is given days after the wedding
When time has past, this gift will be remembered far more than a pot or other gifts you might be considering