Hi, we have a $200 on board credit for our upcoming Med cruise (3 days!) We got it from booking on board during our last cruise and we've never done that in the past so this will be my first time with any sort of on board credit! I was wondering what the credit is valid for--are there any restrictions? Alcohol, spa trips, excursions, etc? Also, does it expire if we don't use it all on this trip or can you use it again on the next one? Thanks.