Lots of restaurants! Inns, taverns, and thermopolia all have food and there were rings of them for all classes and budgets.

Great source: Ellis, Steven J. R. (2004): "The Distribution of Bars at Pompeii: Archaeological, Spatial and Viewshed Analyses", Journal of Roman Archaeology, Vol. 17, pp. 371–384

There were places that common folk could get food and wine like at a popina. Typically, this was a day-time (lunch) stop for a Roman citizen to get food.

People stood and sat in these open-to-the-streets popinae, and bought soup, bread, cheese and wine from the owner.

There were also bars called osterie or trattorie where people could buy and eat meats, and also have sexual intercourse with the inevitably bodacious waitresses who would work as part-time prostitutes.

Source: "A Day in the Life of Ancient Rome", Alberto Angela, 2009, Europa Editions.

What type of cuisine would the average roman eat. Could they afford meat ?