for the details on the RCI soft drink package. You don't need to carry the souvenir cup around. This is a common misconception. You show your cruise card with the sticker on it and they'll give you a standard bar glass of soda. Bottled water is not included.
To me it really isn't a good deal. As Bob said, you won't even break even unless you drink 4 cans of soda a day. We get it for our son since it makes it easy for him to get his own drinks. We don't get the adult package.
Sharing is controlled because they want to see a soda stamped card for each drink. They are not supposed to give more than one glass at a time per person, this to keep someone from ordering 4 glasses of soda and then giving three of them to others.