We did a similar thing to others for Disney for my nieces. Rang the doorbell in the middle of the night with a box that said open immediately in Disney font and a note from “Mickey.” Inside was balloons, ears and t-shirts. Could definitely be adapted to a cruise. My parents and I are taking them on a cruise in 2 weeks so I found fake customizable boarding passes for a cruise on Etsy and my mom put them in gift boxes with gift cards to get mani/pedis before we go. They got them on Christmas along with a beach bag, sun hats, waterproof phone cases etc.