I have a rather unusual question (so mods, feel free to move it to the appropriate forum).

I am traveling with a large group on a long transcontinental domestic flight for spring break. Two of the people I am flying with are desperately afraid of flying, and alcohol is the best solution for them. We have a two hour layover in Atlanta, and I was wondering how the duty-free stores work. Do I need an international ticket to buy a bottle of liquor from them? Could I theoretically take the train to the duty free in the international terminal and buy a bottle of liquor to bring on our transcontinental flight?

Feedback/suggestions appreciated. Thanks!