beware of "cruise lizards"- they befriend you at the bar and the couple both order triples on your round, when their turn comes he goes to the bar and just buys min for you and they sit it out, or better still he has put "his" tab on your bill and by the end of the cruise you cant prove otherwise.
Some people have this down to a fine art because they simply cant afford it.
There are a few cruise ships that do "all in", I think Fred Olsen used to do it.
Tipping at the end of the cruise is another headache unless you state at the start of your cruise to the purser you dont want to do this they will automatically add the tips to your bill.
Friends of mine had quite a hefty bill due to both above when they left the ship and had not budgeted for it, it can come as quite a shock on your first cruise.