FYI
In the past couple of years, most US airlines have tried to cut costs by targeting in-flight meals and drinks. Other US airlines have started charging economy-class pax on international flights about $5 per alcoholic beverage – I’m not sure about Delta, but I wouldn’t be surprised if they have instituted the same policy because they have stopped serving meals to domestic economy passengers (you’ll be able to purchase food on the flight from Atlanta to San Francisco).
Also, I’d make sure that you have at least a couple of hours for your transfer at ATL – especially because you’ll have to first pass through immigration and then travel to another concourse.
Enjoy San Francisco – it’s a beautiful (& unique!) city.