we just got back from a cruise and you are correct: you can't bring booze on board when you do shore excursions; I think ice tea was available in the cafes all the time, but I'm not sure.
I'm wondering if you can pack booze in your luggage when you embark? Highly advised as the drinks are VERY expensive.
You can give it a try as for bringing it on via your luggage; do not try to bring it on via carry on. Some seem to get the booze through, others get it confiscated. As for expensive drinks, I don't think so unless you are a really big time boozer. Call brands of cocktails are $3.95 and wine about $4.50 and up. I am not sure about beer. These prices aren't any more than in a bar here in USA. In fact DH wishes he could call his own brand for $3.95. They get expensive if you order the fancy specialty drinks in the take home glasses. Anyway, we did manage to get some liquor through in our luggage, not much. We didn't want to appear to be a floating bar or liquor store.