It all depends on where you're from. Check out this great map (via Strange Maps, which I've written about before). It charts the -- surprisingly strong -- regional differences when it comes to what exactly you call a soft drink.
As someone from the south (Tennessee), I can definitely attest that we called everything "a Coke." Seriously. Here's a typical exchange at a restaurant -- an exchange I must have had hundreds of times growing up:
Customer: "What kinds of Coke do y'all have?"
Server: "Coke, Diet-Coke, 7Up, Sprite..."
Customer: "I'll have a Coke."
Server: "Okay. It's Pepsi. Is that all right?"
Customer: "Yeah, sure."
