Last year, there was FIRST money as part of the packages which could be used to purchase food at the event. The dome opened it's food stands and the convention center also had stands opened. Selection included the typical stadium food (burgers, hot dogs, pizza) as well as salads and a few other things (can't quite remember).
There are several options other than those stands. Right next door to the convention center (attached to the Omni hotel) there is a food court with lots of selection (Chick-fil-a, Arby's, Blimpie, Don Juan mexican, and more). As for evenings, there is a Hard Rock Cafe within walking distance,
Underground Atlanta has many restaurant options,
Tech Square (accessible by MARTA) also has inexpensive options in a college setting.
I hope this helps.