Despite the recent weaknesses shown in the US economy, the dollar is still king. It’s still widely used as a baseline currency even in far flung places in the world. At the Tibet – Nepal border, you could only pay the visa fee in Nepali Rupees or in US dollars. Euros, Pounds, Francs…not accepted. So no matter where you’re from, it’s advisable to carry US dollars with you. It saved me a lot of headaches and money to already have my own supply of US dollars.
The next most important thing is to have a bank card which you can use anywhere in the world. My account with TD Bank doesn’t charge me any ATM nor foreign transaction fees. In addition to that, they refund me the ATM fees which other banks charge me. In places like Thailand where the ATM fee is about 5USD per transaction this can really add up!
Having a credit card which doesn’t charge you any foreign transaction fees is also really useful to have. My Capital One card works anywhere in the world (although sometimes I have to call them to authorize a transaction) and gives me a near up to the minute FX spot rate. When I was in Iceland, I used this card when I went out for drinks. On my statement, you could see that the price of each drink was slightly different due to the small shifts in the ISK-USD exchange rate over the course of the night.
Lastly, if you do need to call your bank or credit card company, I found out you can call for free via Skype. I don’t know if it works for other nationalities, but my Skype account is US-based and I can call US toll-free numbers from Skype for free. That has saved me loads of money.