Speaking American, Josh Katz’s book about US regional English, is endlessly fascinating to me.
When I was growing up just north of New York City, my family sometimes made a summer visit to my aunt who lived in Massachusetts. As soon as we arrived, she would immediately offer us a tonic (pronounced tawnic). She didn’t necessarily mean tonic water; she was offering us any kind of fizzy, bubbly, non-alcoholic drink we wanted. According to Katz, tonic was the word of choice, particularly around Boston but throughout most of Massachusetts. Today, that word is declining among the younger generation there but is still strong among older people.
About 60% of the country now calls those drinks soda, with that designation particularly strong on the West Coast, in South Florida, and throughout New England (even among the former tonic people in Massachusetts).
Soft drink accounts for 6% around Washington, DC and in Louisiana. Pop is the word across all the northern United States from Washington State through Pennsylvania up to western New York. Coke is your word if you live in New Mexico, all the way through the deep South. Realize that Coke does not necessarily refer to Coca Cola; even 7-Up, Sprite and root beer are Coke. And (for me, this is the kicker) if you live in Georgia across to western South Carolina, your drink of choice is Cocola. Again, you might want Mountain Dew—but that’s just a form of Cocola.