There are a lot of restaurants and bars to go to on the riverside. If you have the time we recommend bopping into the JW Marriott on the Plant Riverside District as the lobby of the hotel has some really neat fossils and exhibits.
With the wedding being at the start of October, a ghost tour would be a fun and spooky way to spend an evening.
If you have the time, Tybee Island is great for a beach day, weather depending.