Argentine restrooms have regular Western-style toilets, but cleanliness standards of public facilities vary hugely. You can find public restrooms in shopping centers, gas stations, bus stations, and some subway stations. Restaurant proprietors often don't complain if you ask to use the facilities without patronizing the establishment, but buying a coffee or a drink is a nice gesture.
There's no guarantee of toilet paper, so carry tissues in your day pack. Alcohol gel and antibacterial hand wipes are also useful for sanitizing you or the facilities.
Restrooms are usually labeled baño or toilette. Men's toilets are typically labeled hombres, often shortened to "H" (men), caballeros (gentlemen) or ellos. Don't get caught out by an "M" on a door: it's short for mujeres (women), not "men." Damas (ladies) and ellas are other labels for female facilities.