Countries in South America have different local currencies. But now-a-days one doesn´t need anymore to travel with, many different types of bank notes, nor with those travelers cheques. Obviously you will need some cash, for sure!
But one or two valid credit cards and bank cards (like Visa, Maestro, ) will work just fine.
There are ATMs everywhere in banks, shops, supermarkets, some hotel lobbies, gas and metro stations. You will not have any problem getting cash, in local currency.
And apart from that you can pay with credit/debit card almost everywhere. I heard about some German credit cards not being able to pay in certain South American shops…, but I believe it is connected more to debit cards. Apart from that, bare in mind that the systems are being constantly updated and such rules improve all the time.
Important: note you pin codes and don’t forget them!
Shortly before beginning of your trip you should contact your bank manager, inform about your trip and note on which day of the month your card is due, or ask the bank for an extra extent on your credit limits, just to be on the safe side.
By doing so you won´t have problems making payments during your South America trip!