These are not usually included in the quoted cruise cost and may cost you dearly. You'll also be expected to tip room stewards and wait staff.
If you're not going as a large group and you might be interested in getting to know your fellow passengers then be sure and inquire about the usual demographics of these travelers. If you're 20 something and it's a baby boomer cruise you're apt to be bored. If you bring your grade schoolers and most of the other kids are in their teens they won't have enough playmates and you'll be their entertainment for the extent of the cruise.
One very important inquiry to make of your travel agent as well is the formality of the cruise that you're considering. If you show up with a suitcase full of swimsuits, shorts and sunscreen only to find out formal dress is required at dinner you're going to be embarrassed or hungry the entire excursion.
If you've long had a hankering for a cruise vacation but didn't think you could afford it - think again.
Especially now with the travel industry struggling mightily to survive in the aftermath of Nine Eleven, bargains are out there. It just might take a little looking.