If people DO try to get you to drink, it helps to arm yourself with some solid responses. Here are some ideas:
When they say: "Why aren’t you drinking?"
You can say: "Because I’m driving home." OR
"Because I’m the one who’s getting the rest of these clowns home safely."
When they say: "Oh, you can have just one."
You can say: "No, if I have one I’ll want more and I don’t want to go there." OR "No, I don’t want to have just one. It’s not worth the money."
When they say: "Can I buy you a drink?"
You can say: "Thanks, I’m not drinking tonight. But I’ll take you up on that next time!"
(Even if you don’t ever plan on taking them up on the offer, it makes the person feel more like you’re WITH them and not judging them for drinking).