IMHO you missed the easiest way to ID a person as 'Southern or Northern'

Iced Tea!
or
Coke -v- coke
Coke is a name brand, when asking for coke we expect Coca-Cola (Southern)
coke is a generic term for a carbonated 'cola' beverage, This cover all 'brown' cola beverages. Same for Soda/pop.

Really wanna get someone going, Offer them a Mr. Pibb when They ask for Dr. Pepper