I created a document that has a different page for each day of our 4-day cruise. For Sunday (embark), it says: It's Sunday and we're sailing to the Bahamas" and has a large photo of Sensation.
For Monday: it sayd "It's Sunday and we're in Freeport" with photos of Freeport excursions and shops, etc...
I'll use a plastic page protector and tape it up to the door, slipping in each day's page.
I wouldn't use balloons, etc, as they will bounce all over and be an annoyance to people trying to walk by