Extremely common, not very strong. Mostly wine.

Viticulture and the consumption of wine was ubiquitous across the empire and it was drank daily by all classes of people, viewed almost as a necessity. Cato writes that even a slave should be afforded a weekly ration of ~5 Liters. In Odes, Horace mentions the practice of serving at a banquet a vintage from the birth-year of an important guest

However, wine was usually diluted with water before being consumed, so it would not be especially strong.

As for other drinks: Beer was known, but Tacitus speaks disapprovingly of it as a drink for Germanic barbarians. The method of producing liquor through distillation would not be invented for several more centuries.

Horace, Odes

Cato, De Agri Cultura

Tacitus, Germania