Bobert - Artbrooks has it right with a couple of additions.

Shots of booze are $4-$5 each as well, so if you have a frou-frou-umbrella drink with more than one shot, it will cost you accordingly.

Most cruise lines figure all the tips into your price, but you'll earn the undying love of the waitstaff if you give 'em a little extra.

Cruise lines don't want you to bring your own booze on board - that's where they make their money - but you can sneak a bottle of "vodka"
on board if it's wrapped up and hidden in your checked luggage.
Absolutely verboten in your hand-luggage. They will take it and return it to you at the end of the cruise. The same with booze purchased in ports of call.

No problem whatsoever with bringing your guitar on. You may need proof of purchase if you bring it, so that customs won't think you bought it in one of the ports.