The drinking age in the United States is 21. Most restaurants that serve alcoholic beverages allow those under 21 inside. Generally speaking, if only those over 21 are allowed inside, you will be greeted at the door by someone asking to see identification. These people are often poorly trained and anything other than a state driver’s license may confuse them, so be forewarned.
Drunk driving is a problem on the highways of America, and South Carolina and Georgia are no exceptions. Always drive defensively, especially late at night, and obey all posted speed limits and road signs—and never assume the other driver will do the same. You may never drive with an opened alcoholic beverage in the car, even if it belongs to a passenger.
As far as retail purchase goes, in South Carolina you may only buy beer and wine, not hard liquor, on Sundays. In most parts of Georgia, no alcoholic beverages are sold at the retail level on Sundays, other than in restaurants that also sell food.