At least in big cities in Argentina, you can pay with dollars in many places. Some shops like big supermarkets even have a sign that shows their exchange rate. (Note that the official exchange rate is AR$200, but the unofficial one is AR$400. You may get a bad exchange rate in some shops.) For buying clothes it may be more difficult because you must negotiate the exchange rate, and they may only accept only US$100 bills, and only if they look nice and is the new model that has a big face. It may be more difficult to pay the electricity bill in dollars.

(In small towns it may be more difficult, but not impossible, specially if you are nice.)