Carnival has a Honeymoon package that you can order. I think you get wine or champaign, special honeymoon glasses and some other stuff. You can go to their website and look under 'gifts'. Tell them you want it delivered to your cabin on whatever day you want to celebrate. Or, you could just make reservations at the supper club on board and that would be a very private and classy way to celebrate!
Happy Anniversary and Happy Cruising to you!