We have been cruising since Sep 2010 and have had no problems using a US Banks, online banking and VISA cards.
We do all our banking on line and use ATM's for local currency. We both have ATM cards, which doubles your daily withdrawl limit. We only use local Bank ATM's, never the ones on the side of the road or in conveniance stores. These can be problematic, especially in Thrid World Countries, and have frequently been found to be logging Account Numbers and PINS.
It just takes some planning when you know you are going to remote
places, to take some extra cash... The US Dollar and Euro are accepted in Mexico
and Central America
, if needed, but local currency gets you better exchange rates
As far as credit cards you need to explore this a little... Cards like American Express charge a 3% foreign transaction charge (Go figure!).
We found Captiol One VISA and our bank, Navy
Federal Credit Union (NFCU) charge no foreign transaction fees
on their VISA cards
The last piece of advice is once you are underway, contact you credit card company every 90-180 days and notifiy them wwhere you are or are going to be. They will shut the cards down if you don't, thinking they have been stolen and being used in a foreign country.