Just be aware that there are only limited items available on the room service menu...
For instance, you won't be able to order a hot breakfast or the dinner entrees from the dining room (unless you're in a suite.)
But fruit, cookies, sandwiches, continental breakfast and beverages are among the things you can order. Some beverages will be an extra charge, just as they are at other locations on the ship. (Sodas, beers, etc.)