One of the best parts about traveling abroad is the ability to purchase goods and services that are different or aren't available in your home country. A lot of people bring cash to convert at exchanges, but it can be a lot simpler to bring plastic. Credit cards -- especially Visa, MasterCard and American Express -- are largely accepted throughout the world. Ask individual vendors if they'll take the payment, but before leaving you should probably also let your credit card company know.
Reason to Contact
Informing your credit card company isn't required, but it makes things a lot easier for you. With identity fraud so prevalent now, a lot of credit card companies are proactively working to combat it by blocking transactions they think are unauthorized. While this is great for people whose cards have been compromised by fraudulent purchases, it can be really annoying when you are the only person using your card (and this can happen even in your own country). Letting the credit card company know about your travels will forewarn it that purchases from that country are not fraudulent, so you don't get declined.
What You'll Need
Have a rough itinerary on hand before calling your credit card company -- just to give it the dates and places you will be. It also helps to have the number to call for the company ahead of time, but you can easily find this on any of the literature it has sent, or on its website.
Most credit card companies either have an automated service that will guide you to the correct options, or you can speak with a customer service representative. It may be easiest to contact the operator or a rep directly -- which may take longer as these lines are often experiencing heavy call volumes. Tell the representative you plan to travel, the dates of your travel, and the places you will visit. The representative can also let you know if there are any service fees for international travel. This is also a good time to ask about the International exchange rates, but bear in mind that they are subject to daily change.
If you have multiple cards, repeat this process for each of them. These calls are good times to do some research as well: which cards will offer better exchange rates. As mentioned, exchange rates change from day to day, but each company will charge different rates to the card, so this research will tell you which card is the best to use while out of town.