B.C.
I drink mostly water. I bought one drink card. It gave me sodas and it gave me Shirley Temples during the shows in the evening. It also gave me fruit juices. Non-bottled water is free. But the water on cruise ships is better than the average city water.
I sailed Carnival. I watch my pennies very closely and I feel the drink card is very worth it. Buy the drink car the morning of the second day. You avoid the sales tax of the port city and you avoid the minimal amount of time the card can be used the last few hours the day you set sail. IF IT DOESN'T INCLUDE SODAS AND FRUIT JUICES, that's a new policy. I don't know if I would buy it then. You'll have to call Carnival to verify.
I would not buy the souvenir cup. I hope you have a wonderful time.
Good luck to you and yours.