The best thing about cruising is that it makes everything easy: it’s easy to see lots of exotic places in one vacation; it’s easy to make friends; it’s easy to relax.

Unfortunately, it’s also easy to waste a boatload of money.

According to Cruise Lines International Association, the average cruiser spends $2,200 per person on a cruise: $1,635 on the fare plus another $565 for onboard costs and shore excursions (that doesn’t include the price of the airfare for those who fly to the port). The fare is supposed to be all-inclusive as the meals and lodging are taken care of.

But with all the extras the cruise lines throw at you once you’re on board — from drink packages and specialty restaurants to tourist excursions and those infernal casinos — an unsuspecting cruiser can rack up a shocking amount of extra costs. If you’re not careful, you can very easily spend more on onboard extras and unnecessary excursions than you did for the original “all inclusive” cruise fare. The result: when you return to land and get the final bill, you find you’ve effectively doubled the cost of your vacation. Now that’s a bitter homecoming.

So it helps to be prepared. “Our best piece of advice is to do your research in advance and familiarize yourself with what’s included in your base fare, and what’s not,” Carolyn Spencer Brown, editor-in-chief of CruiseCritic.com, tells Yahoo Travel. “By preparing in advance, you can pick and choose which costs are worth your while, without being caught off guard once you’re already onboard.”

Your pre-cruise preparation starts now. Here are the top five ways people waste money on cruises.