By now, you’ve probably taken a flight or two, and you feel like you’ve got your travel game down. But even if you do know all the tricks for getting great deals on hotels or know the best time to book a rental car, there are still more than a few travel surprises that can pop up and ruin your trip.

If you want to avoid getting stuck without cash or trapped in a foreign country with someone staying in the room you paid for, you might want to pay attention to these 10 tips. They’ll help your vacation stay stress-free. Plus, you’ll find a couple of new ways to save money—and get a bonus or two added to your stay.

Know the “Six Months Validity Rule.”

Sure, you know you need to have a passport to travel outside the country, but how often do you check your expiration date before you head abroad? It turns out that, even with a valid passport, you still could have problems getting to your destination.

Many countries require visitors’ passports to have at least six remaining months of validity in order to enter. So if you plan to go to Brazil tomorrow and your passport expires four months from now, you probably won’t be getting on the plane. This isn’t the case for every nation, so make sure you check the passport requirements well in advance of your trip. You can find all the countries with this policy here.

Figure out your service.

It’s easy to forget that your phone won’t work in another country. Well, sometimes it works—you’ll just be charged huge roaming fees if you’re not careful.

Going without cell service doesn’t sound like a big deal, but remember, it means you won’t have GPS or Google to help you if you get lost or end up in the wrong part of town. Make sure you print out any necessary maps before you leave, just to be sure you know where you’re going in case there isn’t wifi to be found.

If you want to be able to use your phone abroad, consider buying an international plan. This is best if you’ll be overseas for a long time or if you need to make business calls during your trip. Even if you don’t want a plan, call your phone company to find out how you can configure your phone so you won’t be charged accidental roaming fees.

For a cheaper way to stay in touch, install WhatsApp. It’s a free app that uses wifi (or data) to let you text all over the world. Just make sure you install it before your trip—the app uses your phone number for verification, and you’ll need to have service to set everything up. But after that brief setup, WhatsApp will work pretty much anywhere you like.

Give your bank or credit card company a call.

When your credit card company sees a charge from, say, Belize, it will often suspect fraud and block the charge. If you’re vacationing in Belize, though, this will make your life pretty difficult.

Instead, call your bank or card company in advance, tell them where you’re going and how long you’ll be there. It usually takes less than five minutes and insures that your card will work throughout your entire vacation.

David Bakke, traveler and writer for MoneyCrashers, says there’s another important reason to call: it can save you money! “Be sure to check all of your credit cards for free travel perks you can take advantage of, which will vary by provider,” says Bakke.

Oh, and while you have them on the line, ask them about their foreign transaction fees. Some have low or no charges for when you use your cards overseas, but others add substantially more to every purchase. If you know their foreign transaction fee policy, you’ll save yourself a ton of money during your trip abroad.

Keep your rental car in the loop.

Usually, you send your flight info to your phone, your loved ones, and whoever’s meeting you for dinner after you get off the plane. Rarely—if ever—do you think to let your rental car company know your flight info. But when the rental car company is out of the loop, you risk a canceled car.

If your flight gets delayed, the rental company will usually hold your reservation; If they don’t have your flight info, they’ll figure you just didn’t show up and cancel the reservation. Once you finally do get to the counter, you’ll have to rebook at a higher fee or risk not having a car.

Give the rental company your flight information when you make your order. Even with a late flight, you’ll likely still have a car ready and waiting.

Find out if you can ski for free.

Jesse Ambrogi-Yanson of Ski.com has a tip that gets you a great vacation bonus.

“Ski … for free [the day you arrive] when booking with certain airlines that partner with resorts,” she says.

“Fly Alaskan Airlines, for example, and ski free on the day you arrive at Sun Valley and at Schweitzer,” she says. “Receive free night skiing on your day of arrival when flying into Steamboat/Hayden on Alaska Airlines, or ski free on your day of departure.”

Even if you’re not flying Alaskan Air, you could still get some extra time on the slopes.

“Keystone offers free night skiing the day of arrival when lodging is booked at participating resorts,” says Ambrogi-Yanson. Also, kids 12 and under ski free for your entire Keystone trip as long you stay two nights or more.

“Guests arriving at Squaw/Alpine Meadows via a commercial airline can ski or ride on the day of their arrival for free,”Ambrogi-Yanson continues. “Just pick up your ticket at the new ‘Mountain Concierge’ store in the Reno airport.”

So, if you’re heading to the mountain and want some bonus time in the snow, check for free deals before booking your trip.

Be wary of room sharing sites.

Room sharing sites like Airbnb are great; you get to save money and live like a local wherever you go. But they do carry a greater risk than traditional hotels.

With a regular hotel, you have a staff devoted to helping you, and it’s rare that you’re ever left without a room. With room shares, if the owner gave you false information, the room isn’t up to standards, or you have any other problems, there’s less that anyone can do.

Shy Bredewold of Odyssean Travel says that “when they go wrong, they really go wrong.”

“I’ve heard all manner of tales,” Bredewold says, “from no-show with the keys to ‘whole apartments’ being shared spaces, and plenty of extraneous bills, including my favorite: ‘too long in the shower.’”

One time in particular, Bredewold faced a room-share nightmare.

“I showed up and there was already someone in the room! The host had failed to issue the updated information to the platform,” he says. “In a less densely populated area or country with more extreme [communication] barriers, this would be catastrophic.”

Bredwold’s trip isn’t the norm, but it isn’t unique. If you’re in a country that you’re not familiar with or you don’t speak the language, a room share might not be the best option. Winding up without a roof over your head in an unknown location isn’t a great way to start a vacation.

Turn a layover into a vacation.

Usually, most of us avoid layovers like the plague. They make plane travel even longer, and you usually wind up marching down the aisles of the duty-free store and contemplating buying a huge Toblerone for no reason. But they don’t have to be horrible.

Aaron Mandich of Flight Baron says to make the layover part of your vacation

“If I know I will already have an awkward layover length (over two hours and under five),” Mandich says, “I will purposely purchase a ticket with an even longer layover, giving myself more time to go out and see a city.”

Especially on long international flights, layovers are unavoidable. But when you purposely make them longer, you get a chance to see an extra city during your trip without having to worry about spending for an extra hotel stay.

“I once gave myself 8.5 hours in Paris. Enough to climb to the top of the Eiffel Tower, have a French lunch, and eat a crepe for dessert,” says Mandich.

Now, you do need to keep a couple things in mind if you are going to take a layover-vacay. First, if you’re visiting a foreign country, you may need a visa. The U.S. Department of State has all the info about travel requirements for any country you might like to visit.

Also, give yourself extra time. After your little trip, you’ll essentially be checking in all over again. It’s not hard, but it can take a while. Layover Guide recommends giving yourself ample time, since most international airports are huge and it may take a long walk and a shuttle ride to get to your gate.

Oh, and definitely don’t miss your flight.

Be careful with your souvenirs.

You can buy as many “I Heart NY” mugs as you like without doing any damage. But some souvenirs from around the world can actually be made from precious materials—that are illegal in the states.

“One thing many travelers don’t know and can get themselves in trouble with is purchasing souvenirs made from endangered turtle shell,” says Brad Nahill of SEE Turtles, a non-profit who works to protect the creatures. “These are banned from bringing across borders, illegal to purchase in most countries, and come from the shell of the critically endangered hawksbill sea turtle.”

This may sound incredibly rare, but sea turtle souvenirs are commonly sold in Latin America, the Caribbean, Southeast Asia, and parts of Africa. If you’re not sure what sea turtle shell looks like, check out Nahill’s guide. It’ll help you avoid purchasing something illegal and help keep an endangered species safe.

Outside of sea turtle souvenirs, there are a few other international items you’ll want to keep out of your suitcase. Generally, it’s best to avoid bringing any food back from a foreign country. Fresh foods can contain dangerous pests, so you have to declare it when you’re coming through customs. Any undeclared produce will be confiscated.

Haggis from Scotland or a Kinder Surprise Eggs from Switzerland are both illegal to bring into the States due to violations of food safety laws, and similarly, you aren’t allowed to bring coca tea from South America for the reason you might expect. Oh, and dried soup mix—most meat products aren’t allowed, so even the tiny bit of meat in your overseas Top Ramen can’t home with you.

Check your passport stamps—a stamp from Israel might halt your trip.

As you travel to different countries, you get more stamps on your passport. This is usually a cool way to look back on all your journeys and brag about all the traveling you do, but a stamp from Israel might actually stop your vacation in its tracks.

Khanh Tran, marketing communications executive of Villa-Finder with years of experience helping customers travel around the world, has this advice: “For those who visit Israel, it’s better to ask the Customs Officer to stamp on the immigration paper available at the airport rather than stamping directly on the passport. … having an Israel stamp may give you some difficulties when entering/applying visas to Islamic countries such as Indonesia in subsequent travels.”

A stamp from Israel won’t impede any travel to North or South America or Europe, but it can make it difficult if you’re going to the Middle East. In addition to Indonesia, Lebanon also won’t allow entry to anyone with stamp from Israel on their passport.

Get your shots.

We’re not just talking MMR, here. Many countries require you to get particular vaccinations before you ever step on a plane. According to travel writer Anne Steinbach, most African nations require a yellow fever shot before traveling.

“Fun fact,” she adds, “when traveling to Côte d’Ivoire and you do not have the vaccination, you will be escorted to a room and get the vaccination there. Not the best experience, I must admit.”

The CDC has more information about the vaccines you’ll need to get before you go to specific countries.