Another thing to do, is bring a travel mug so you can fill it with iced tea to bring to the pool, etc. You can also make some good iced coffees that way. I bring a giant mug and I bring some Crystal Light. Since the staff fills your ice bucket twice a day, you never have of ice in your cabin,
Bringing your own alcohol poses a problem for any business that is serving alcohol...it is all about accountability for the business...over-serving and all the problems that can be a result. We have a liquor license so we spend a great deal of time training our staff.
I know a couple of years ago, there were major problems with some of the cruises over-serving, so I applaud them for trying to control it.