When I am at a restaurant and do not know what brand beverages they serve (i.e., Coke, Pepsi, etc.), I will just ask the waiter/waitress for a "Coke or Pepsi," "Sprite, Sierra Mist, or Seven Up" "Dr. Pepper or Mr. Pibb," etc. If I slip and say "Pepsi," the waiter/waitress usually asks if Coke is okay or vice-versa.

Growing up as a kid in MD with Coke products around the house, I said Coke (even the restaurant served Pepsi).