Before smartphone there were physical cruise cards, which are still a reliable and whimsical way to swap info.
Keep some in your pocket to give out to others.
Put some into a basket outside your door for others to take.
It’s also fun to collect them!
Leave a space to write in your room number later if you want to reuse the cards for a future cruise, or if you don’t want (all) your cards to have your room number on them.