You should definitely buy travel insurance! It can help you recoup any losses you might have should your flights be cancelled and you miss the cruise (there are restrictions, so be sure to check the policy details), and can also help reimburse you for expenses should you have a medical problem that needs treatment while on the cruise. There are often other coverages, such as for acquiring some basics if your luggage is lost, etc.
As far as bringing a cooler of drinks onboard, chances are pretty big that it would be confiscated (and returned to you at the end of the cruise). There are other threads on this subject on this forum, which you can do a search for.
Not sure what you mean by "what to do in advance" - packing? other preparations? I would advise having a passport; the time is coming shortly when everyone will be required to have one to get back into the U.S., and you have plenty of time to get one before your October cruise. They last for 10 years and if you have one, you don't have to mess with the certified birth certificates, etc.