On cruises – Most cruise lines add tipping, also called gratuities, to your shipboard account or tipping is included in your all–inclusive experience. Some still leave tipping up to your own discretion. In that case, plan to tip $2 to $3 per person, per day (for a total of $84 on a seven–night cruise) for each person in your stateroom. On shore excursions, tip $2 to $5 for the tour guide, and $1 to $2 for the driver.
At resorts – It is customary to tip for good service in the U.S. Most tip 15%–20% on food and beverages. For exceptional service, tip up to 25%. When staying at an all inclusive resort, tipping is already included. However, your favorite bartender or server always appreciates a little extra, especially at the beginning of your stay.
At airports Tipping your skycap is a good thing. If they check you in curbside, tip $1–$2 per bag. If they take your bags inside for you, tip $2 per bag. If your bags are extra heavy, add in a little extra. If you don't have any small bills, ask if they have change. Chances are, they have a pocket full of singles and can gladly make change for you.
International - Many countries do not tip or tipping is at a much lower rate than in the U.S. I recommend doing research on the country's customs before traveling to ensure you are tipping or not tipping appropriately.
This information was copied from http://tbodell.cruisesinc.com/travel/cruises/Editorial.html?edType=Custom%20Page&pagename=travel-tips