When we went on our first cruise a friend suggested that me and my fiance share our soda package. We only bought one it went on my fiance's seapass (the sticker)we were together when we bought the one for him. Even if I used his seapass waiters still gave me the soda, we shared openly and no one ever said anything to us. Since then we have just shared on cruises.
There might be actual rules out there for it I am not sure I will try and find something