Do NOT rely on a MasterCard!! take Visa!!! i have travelled extensively all over the world, and fortunately i carry both cards. At home i use the M/C, but I have found there are countries where it is not accepted, or you have to go to great lengths to find a bank that will deal with it! Use your debit, as mentioned above. M/C is definitely not popular in central and s. america! Sometimes even your Visa is not acceptable, so make sure you always carry some real cash in euros or u.s. banknotes... and even tho travellers cheques are no longer popular, they can be insurance in an emergency.
In Mali, i was told i could pay for my onward ticket to Senegal by Visa. I was leaving Africa, and had little cash left of any kind. I had used up my dollars, euros and travellers cheques.. but when i got to the airline office, they said NO to Visa, cash only! I had enough for my ticket, but my travelling companion was out of cash. they sent us to the bank next door that had a bank machine. It didn't take Visa or M/C or debit. I went to the desk and requested an advance on my Visa (i have done this before in other african banks). Bank lady went away for ten minutes and came back and told me my account was overdrawn. It wasn't. I have a high, unachievable (for me) limit. I then had a major meltdown (in verbose, scatalogical English) , much to the amazement/amusement of the bank guards and various customers
We managed to scrape together enough money to cover our tickets....and then he went on a search of Bamako for a machine that would accept a Visa card for enough money to pay me back, and cover the rest of our time in w. africa. It took some time, but fortunately he was successful...but it could have been a disaster...
I actually had enough cash for myself, but couldn't abandon my fellow canayjun travelling companion...even tho we had only met on the plane that morning!! ...that's the way it goes sometimes!!