Cruise ship spas typically have not only treatment rooms but also saunas, steam rooms, and thermal relaxation suites. Most lines waive the access fee if you book a treatment — which is why it's surprising when you get a $200 massage and don’t get access to the facilities. On Royal Princess and Regal Princess, for example, you should be prepared to pay about $50 more for spa access.

The Solution: If you're not getting a treatment, but want to use the thermal suite, booking a multi-day pass may be the best deal. In addition, Viking Ocean Cruises doesn't charge any fees for passengers who what to use the saunas and steam rooms — whether you're getting a massage or not. 

Once largely complimentary, some room service order now come with charges on major lines. Up until last year, Carnival had never charged for room service. Now, the line has introduced a fee for new menu items like personal pizzas and quesadillas (other items are still free of charge). On Norwegian, a $7.95 convenience charge will now be added to your bill unless you’re staying in The Haven, the line’s exclusive spa-level accommodations. 

The Solution: Some lines, including Disney and Holland America, maintain complimentary room service, though gratuities are not included and there are additional charges if you are ordering alcohol. Royal Caribbean and Celebrity add a charge of $4 or $5 if you order late or overnight (typically between 11pm and 6am). Room service on Princess is complimentary, unless you are having a pizza delivered (a $3 service fee) or if you are arranging an Ultimate Balcony Dinner, which involves a five-course meal and Champagne ($50 per person).

If your cruise ship has a fitness center, you’ll have free access to all the weights and treadmills you want. But signing up for a yoga or spin class? That’ll run you around $10 on lines like Carnival, Celebrity, and MSC. And on Cunard, yoga, spin, and boot camp classes range between $12 and $18 apiece.

The Solution: Some cruisers bring a DVD of a yoga routine, and take their laptop to the gym so they can use the mats for their own private "class." This also ensures the skill level of the class is right at your level. 

If you’re cruising to Rome or Florence, your actual port of call is in a different town altogether (Civitavecchia and Livorno, respectively). Even worse, the cost of this transfer isn’t always included in your fare. Cruise lines like MSC and Carnival offer excursions into the city that are often more expensive (though more reliable) than booking your own train into the city. 

The Solution: If you're with a group of four or more people, compare the cost of private transfers to what the cruise line offers — you may get a better deal, and a more custom experience. 

It's no shock that alcoholic beverages will cost you extra, and on most lines the prices aren't so different from in restaurants back home. (You’ll have to pay around $2 per soda as well, plus a 15 to 18 percent gratuity charge.) Still, the numbers will start to add up. 

The Solution: On Disney Cruise Line, soda flows freely at poolside drink fountains. Otherwise, how do you save? If you’re planning to drink three to four sodas a day (or more), an unlimited soda drink package (which costs $6 to $8 per day) might be for you.  

You can also plan ahead: Some lines, including Carnival, will allow guests to board with a 12-pack of soda, while both Princess Cruises and Norwegian Cruise Line have no restrictions on packing your own nonalcoholic beverages.

If the price of fuel jumps, you just might be the one to pay for it. Some lines, including Royal Caribbean and Cunard, reserve the right to charge you up to $10 per person per day without prior notice — but only if the price of fuel rises above $65 per barrel. That’s regardless of whether yours is an existing booking or a new one.

The Solution: Some lines, including Carnival Cruise Line and Norwegian Cruise Line, have eliminated fuel surcharges.