You would only pay extra IF you order items that have an upcharge, or if you order more than the items included in the Free at Sea meals.
There have been recent reports that the FAS meals include the following: 1 Appetizer, or Soup, or Salad, and one Entrée, choice of two sides, and 1 Dessert. Others have reported being able to receive fewer choices. And others have been allowed more choices. However, below are NCL Terms and Conditions:
Applicable to guests 1-2 on the reservation
Dining package is applicable to guest ages 2 and older
Package prices are subject to change
Guest is responsible for 20% gratuities on the retail value of the Specialty Dining Package prior to cruise
20% gratuities on the retail value of the Specialty Dining Package are included when booking through the Australia office
For Casino booked reservations – promotion code CASFAS will be added under referral code CASUPALL on sail lengths 7 nights or longer for Balcony and above staterooms
Packages are based on a per meal basis
Any Harvest Caye bars, restaurants, or venues, The Bake Shop, Ice Cream Bar, Gelato, specialty items in the Asian restaurant, Special Occasion/Holiday menus (New Year's, Christmas, etc.),
Jazz Brunch, Wine Lovers and Murder Mystery lunches, and beverages are not included as part of the Specialty Dining Packages
Guests are permitted to pre-reserve specialty dining with entertainment included However, the guest is responsible to pay the full retail value
If the guest chooses to use the reservation as part of their specialty dining package, they will need to make these arrangements once onboard
Specialty Dining Packages include one main course per person at Cagney's and Le Bistro
Additional main courses will be charged at the a la carte price listed on the menu
There is no minimum or maximum to the number of meals that can be redeemed in a day, however each meal is counted towards the package