I have done both ways. If you use the gift cards prior to boarding, you will have to call to make it happen because there is no option to use a gift card to purchase. If you wait until you are on board and have not already added the gift cards to your account, take photos of your gift cards because they will take the paper copy and it will take an hour or so to apply to your account. Also of note, if you have purchased the insurance, if you add the fare package prior to sailing, it increases the cost of the insurance but if you wait until you are on board, it does not.