Sounds like a great time.
I have a group that I met on a cruise, and we have had reunions. I send countdowns.
Then daily I send an e-card/photo.
How about some port related stuff. Not sure where you are going, but, for example: tropical drinks for Caribbean, Corona beer for Mexico,
sunscreen, lanyards for your cruise card, disposable camera, or even an underwater camera, a small photo album.........
Happy 40th & hope you have an awesome cruise