Being a native Okie (now transplanted to Phoenix), I've inherited the South's generic "coke" with the rest of the nation's interpretation of "Coke specifically means Coca-cola."
in reply to I refer to a non-specified carbonated beverage as a:
In Oklahoma, when one makes a suggestion to retire to a soft drink establishment, one says, "Let's go get a coke." When ordering a "coke," Coca-Cola is served. Sort of a polymorphic, context-sensitive usage of the word... :-)
"Soda" invokes images of the canadian border and "pop" just sounds weird to me...