In most cases, gratuities are already added to your bill, usually at the rate of say, $11 per day per person, depending on the cruiseline.
Drinks are free, except for alcoholic beverages.
Have fun!
Keep that in mind. I've seen where, at the end of a cruise people end up owing several hundred dollars on drinks alone. At $5-12 per drink, it can really cost you. If you have a beer with lunch, and say 2 drinks with dinner and then 3 more drinks per day.
So $5 for a cheap beer, or a bit more for a specialty beer. Then 2 dinner drinks at $20, then another $30 during the day. You're at $55 per day, or $385 in drinks, is already more than half of the $1300.