I'm not in Snellville but I've had some bad experiences OCing in Walmart in various other parts of the state, especially Statesboro. All those experiences were late at night and involved one manager who did not know their policy.
Public gatherings include (but are not limited to... love that part of the statute) athletic or sporting events, churches or church functions, political rallies or functions, publicly owned or operated buildings, or establishments where alcohol is sold for consumption on the premises.
You MUST have a valid license to OC in Georgia. You can thank Jim Crow laws for that.
We also have some interesting caselaw in GA... namely Farmer v. State, which states that a firearm accessible in a vehicle up to 200 yards away from a public gathering is still a violation of the law, and State v. Burns, which states that McDonald's is not a public gathering, and that the legislature differentiated between "public gathering" and "place that is open to the public".
If you search on georgiapacking.org we have quite a bit of discussion of open carry.
Disclaimer: I am not a lawyer, your experience may vary, not for consumption by women who are pregnant or who may become pregnant, MSRP plus tax, tag, and title, management assumes no responsibility for damage caused by carts left in parking lot.