5. Pack smart.
Savvy travelers who pack well can save a lot of money on last-minute purchases. This sounds like a given, but when you're packing, it's easy to talk yourself out of bringing more stuff, thinking that you probably don't need it. If there is just a remote chance you might need it, put it in.

Things like that extra bottle of sunscreen, bug spray, an umbrella, a rain jacket or a sweatshirt will be very expensive if you have to buy it on the ship or in port. Also, consider bringing coordinating layers of clothes, because, while many destinations are quite warm during the day, it can get cooler in the evenings, and air-conditioned areas on the ship may be quite cool.

6. Track your drinking and gambling.
Alcohol and casinos are two major cruise line profit centers, and many passengers get carried away with both. If that's how you plan to relax, fine, but be aware how potentially expensive both activities can be.

"Some onboard casinos offer free gambling lessons where you can play craps and the other games with play money," says Eggers. "It's a way to get the experience of gambling without spending money."

As far as soda goes, many cruise lines are offering a flat-rate soda package for adults and children for the entire voyage. You pay one fee and get as many sodas as you like instead of each one costing $1 or more, Entin says. Frequently, ships offer an alcoholic drink special of the day that will be discounted and a bit cheaper than other drinks, Eggers says.

7. Watch out for photos.
Shipboard photographers will snap your photo when you board and frequently throughout the voyage. Usually you have to buy a package of photos, rather than just one, so the cost can add up, says Miller.

"When I started cruising years ago, the photos were $2.95, then they went up to $9.95 and $12.95, and now the packages go for close to $20," says Entin. She recommends that you take a camera and shoot your own pictures. If you want photos of your group, friendly co-passengers will usually oblige.

8. Don't prepay tips.
Tipping is an expense that can really add up. Passengers are expected to tip both their cabin attendant and assistant cabin attendant and regular waiter and assistant waiter daily. Recommended rates vary according to the cruise line, but $3.50 a day is generally expected for the cabin attendant and $2.50 a day for the waiter.

Some cruise lines allow you to prepay your tips on your shipboard account, which removes the hassle but doesn't give you the opportunity to reward outstanding service or penalize poor service.

9. Call home in port.
Using the Internet or phone while on board a ship can be incredibly expensive, says Entin, so save your calls or e-mails for when you're in port. "I find an Internet cafe when I get off the ship and check in that way," she says. You can also buy prepaid phone cards so that you can make calls in port as well.

10. Check your account balance.
Charging all of your extra expenses to your shipboard account is convenient, but when you don't stay on top of your bill, you can get a major shock when it comes time to pay. Some cruise lines offer you the chance to look at your bill on your cabin television so you can keep closer tabs on it. If not, you can go to the purser at any time and ask to see how much you're spending.