Before arriving in a country you should have some local currency to ensure you don't get stuck on arrival. The most popular options of foreign currency include cash, traveller's cheques and credit or debit cards. A combination of these is a great idea as it offers the most security.
It's also very worthwhile to find out whether there are Automatic Teller Machines (ATMs) at your destination. You will have to confirm with your bank that your card will work overseas. Do some research on the currency exchange rates before you leave for your trip to make sure you do not get taken advantage of on any of your travels.
It's important to remember that many countries will require you to pay a departure tax, which is payable on leaving the country. It is important to note that you will have to have enough local currency or convertible cash to pay the due taxes.