Hello... If I were you I would go and bring a lot of bottled water or whatever your drink of choice is, or candy whatever. You won't know what you are like at a party sober until you try it for yourself. And I would imagine, when you see how people act when they are intoxicated it will give you a new understanding for how you use to behave at such functions. I personally would just say "No Thanks." and leave it at that if someone offers you alcohol. If they pressure you and keep on trying to get you to give in, politely tell them you are trying to give drinking up.
If you are anything like I am, that ONE drink will lead to another and the more you have the more your inhibitions are weakened. Just think about how great it will feel to not give in to temptation and work on increasing your willpower to say no. You said yourself that Saturday would be a big test, so think about how great you will feel the next morning.
I know i'm new and feel like i'm the last person to give advice (or I wouldn't be on this site), I am just offering my personal opinion on what I would do. Good luck Saturday, you can do this!!