In the military (doens't matter which service) you meet folks from all over the country, and even from US territories.
I heard the different names for "carbonated beverages" (no hard and fast rules, of course) .
Midwest (where I'm from), SODA
Northern middle states (MI, MN WI) POP
East coast: POP
South: COKE... yep all soda was called Coke; how you actually differentiated between, say a Pepsi and a Dr Pepper, I have no idea. Also a "Soda" meant an ice cream soda.
SW (where I am now)... because there are so many transplants/snowbirds here from other states and also Canada I hear SODA and POP about equally.