With credit cards becoming more acceptable and ATM machines available in nearly every city of the world, traveling with cash is not only unnecessary but can prove risky because of possible loss and theft. However, you may still wish to bring currency if your journey takes you to more isolated regions, if the local currency is devaluing quickly or if you want to give American dollars to friends and relatives living abroad.
Carrying reasonable amounts of cash is no different on an airline than in a private car or public bus. You can keep them in your wallet or purse for easy access, as long as you exercise reasonable care. In other words, don't ostentatiously display large bills where they can easily be seen. Though thieves have nowhere to run on an airplane, they can just as easily pick your pocket without you finding out.
You can travel within the United States or leave the country with any amount of cash. However, certain countries may restrict what you can bring in, so always check with the embassy of your destination location.
If you withdraw $10,000 or more from a financial institution, you need to file a copy of FINCEN Form 104. In addition, you need to complete Customs Form 4790 when carrying $10,000 cash out of or into the country.
Note that although you may not be carrying close to this amount, airport security officers may question you about large cash amounts due to concerns about drug and terrorist financing. Any documentation you can provide, such as a copy of Form 104, can help allay any suspicions.
Never keep cash in checked-in luggage or even in carry-on bags that you may leave unattended. Instead, always keep money on you, preferably in several separate areas like in a money belt, passport pouch and wallet. If you're traveling with a partner whom you trust, give him or her some of the cash as well. That way, if one of your stashes is lost or stolen, you will still have most of your currency with you.
If you intend to use or exchange any of the cash at a foreign destination, keep in mind that smaller denominations are easier to buy or tip with, while larger currency gains you the best exchange rates.
