Pop almost always.....sometimes Soda but never the generic "Coke".....
We used to have a store here in Indy years ago that sold a variety of carbonated drinks in mix and match cases in returnable bottles called "The Pop Shop". It was a great deal. After the bottle deposit it cam out to about 9 cents a bottle.
I'm a waitress and one time when I asked a guy what he wanted to drink, he said "soda water." I gave him a puzzled look (as I was thinking he must want baking soda mixed into a glass of water!), and his wife rolled her eyes at him then turned to me and said "he wants a Coke." Why didn't he just SAY that then.
In the TX/OK area you're most likely to hear the term "cokes" when people are speaking in general. Soda probably comes in second, but pop, sodapop, and cola are not totally unheard of around here.
I have never heard it called tonic by anyone until this thread.
I don't use if often, but I like the term sodapop best. It sounds so bubbly and old-timey .