That is a good question and one that doesn't have a definitive answer. If you won the cruise the then the following is included:
Cruise for Two that includes taxes and gratuties
Airfare for two (you will have to pay for extra bags beyond what is included)
Motel Room night before the cruise
Transportation from the hotel to the port, from the port to the airport upon return
You will likely be responsible for your transportation from the airport to the hotel. I will see if I can find out about shuttle service availability or taxi fares. I believe last year it was about $20 in a taxi from the airport to the hotel, but I am not sure how far it is this year since we will be leaving out of Galveston and last year we were in Ft. Lauderdale.
While on the ship anything you buy in the stores, any drinks (sodas and alcohol) than the ones that come with meals (tea, coffee, milk, juice), any amenities such as spa service are charged to your room and then charged to your credit card at the end of the cruise. You are responsible for those charges.
Any shore excursions are your responsibility. There are some listed on the Royal Carribean site, LAND SHORE EXCURSIONS, if you would like to check them out. There are a total of 171 excursions to choose from on the list so make sure you click "next page" to see them all. Last year we didn't do any excursions but there were plenty of people that did and enjoyed them. Sandie, Karen, Sandy and I all preferred to do our own thing and explore on our own. There are some suggestions on the 2012 Cricut Cruise from members who are doing the Dunn's Falls or the Mayan Ruins.
There is always plenty to do on the ship. There are 4 pools on the ship, one being an adult only, which is what I prefer since I will not be taking any children with me. There are also a total of 6 whirlpools on the ship so there are plenty of places to soak up the sun. Last year we were given a list of available activities every day so we could choose what we might like to do. Several people enjoyed the nightly entertainment in the live theater, that included magic shows, dancing, etc. There is a cinema on board where you can go watch a movie. There are night clubs available if you want to dance the night away. The Mariner of the Seas also includes a Rock Climbing Wall, Miniature Golf and an Ice Rink. I know there are a lot of things I am not mentioning but I just wanted to provide some highlights. At this time I do not know which of these might cost extra.
If you choose you can leave extra money for a tip at the end of the trip and an envelope will be provided for this. Karen and I each left extra in the envelope because our stewards were so awesome!
Anything you buy while on shore is at your own expense, such as eating, shopping, excursions, etc.