I just checked with Princess the other day. They said the Coke stamp was $4.95 a day. And if you like coffee drinks they have a coffee card that is $24.95. it gives you 15 drinks for the price of 12. Both the coffee card and the coke stamp will have a 15% gratutity added.
Bon voyage :-)
Next Cruise - Grand Princess may 2013 Alaska
8- Carnival Splendor
7- Sapphire Princess
4-Royal Caribbean-Monarch of the Seas
2-Carnival Spirit-Richard Simmons Cruise to Lose
1-Carnival Inspiration - Richard Simmons Cruise to Lose