Regional vocabulary. In California, I buy a soda. Not a pop. Not a soda pop. and a coke is a Coke™, not any carbonated sweetened beverage/soft drink.
Well if we consider the rule of first mention ... Pepsi Cola was created in New Bern, North Carolina. Coca Cola was created in Atlanta, Georgia. Royal Crown was created in Columbus. Georgia. Doctor Pepper was created in Waco, Texas. So since many of the major carbonated beverages came from the south, let's go to a well known southerner who was always good with describing things to see how he said it!
Pop here in the Chicago area. My wife grew up in California, so she says soda. And yet we make it work.
First, you people are all heathens. Secondly, this is a test I've used all of my life to tell when we have foreigners about. Foreigners meaning, anyone outside of the NW. Why? Because it's called coke people. Little c. You want something to drink? Yes, I'll have a coke please. What kind, we have orange, root beer and 7-up? Do you have grape? No. Just a regular coke then please. Soda? That's bubbly water. Pop? Leave your Dad out of this.
And the purple lips to go with it. Remember when you could buy a Nehi out of a big lift top cooler. You put your money in and you slide the bottle along the tracks and pop it out of the gate??
Coke in my area. I'd be afraid what I'd get asking for a pop around here. They might give you one for sure.