Included in your cruise fare: Main dining room, Windjammer Buffet restaurant, Cafe Promenade. Note that there are some extra-fee items at Cafe Promenade. And finally, room service is available 24 hours a day except on embarkation day and debarkation morning. (But read below for more on room service)
Extra cost: Johnny Rockets diner ($4.95 per person cover charge includes all the food you want but specialty sundaes and milk shakes cost extra - beyond the $5), Chops Steakhouse ($25 per person), Portofino Italian ($20), Room Service deliveries from midnight to 5am have a $3.95 per delivery surcharge which includes tip.
There is also a Ben & Jerry's where everything has a price.