Sorry, but once again I have to state that I think that the soda-stamp deal onboard is a rip-off. Ture you get this cute SMALL soda cooler-tumbler type holder, but, once filled with ice, holds MAYBE half a can of soda.
On our last trip, I found that using my sea pass card account, I could buy a whole can of soda for about $1.50 each, and they would give you a glass if ice too if you asked.
On our first cruise, we both bought the stamp for about $85-$90 for both. We ended up maybe dringing three full cans of soda each for the entire 7 days-so unless you are a major soda drinker, I'd pass on the stamp. It just seemed like an unnecessary expense, and , in my opinion, a large money maker for the cruise line. Use the extra cash you save for something nice to remember your trip (photos are another big expense, but at least you have something nice to look at and remember)
Iced tea (for those who like it), is free.
Have a great cruise!!