Credit cards are invaluable when traveling. They are a safe way to carry money and provide a convenient record of all your expenses. You can also withdraw cash advances from your credit cards at any bank (though you'll start paying hefty interest on the advance the moment you receive the cash.) At most banks, you don't even need to go to a teller; you can get a cash advance at the ATM if you know your PIN access number. If you've forgotten yours, or didn't even know you had one, call the number on the back of your credit card and ask the bank to send it to you. It usually takes 5 to 7 business days, though some banks will provide the number over the phone if you tell them your mother's maiden name or pass some other security clearance. If you are using a credit card abroad, keep in mind that your credit card company will likely charge a commission (1 or 2%) on every foreign purchase you make.
Outside North America, the most commonly accepted credit cards are MasterCard, Visa, American Express, Diners and Discover, in that order.