Moral dilema

I was invited to a 21st birthday party of a girl in my class. Funnily enough, this is the first party I have been invited to literally for years. How did I manage to make it to the "cool" group without even trying? All those years in early high school, I wanted to be regarded as "cool" or the one that everybody laughs with about silly jokes. I am the one now that everyone involves in conversation, a person that people tell things to, includes in jokes and so on. Yet, it's funny because it's really not that great. While I really like and appreciate my new set of friends, I recognise that they will probably never be the kind of friends that I would tell my deepest, darkest, personal secrets to.

Anyhow, flattered by this invite, I am -- but I'm unsure if I really want to attend. I sort of obliged by telling her I would come, but the girls in my class who are going are organising to all get a cab together so that they are able to drink and are organising to stay at a motel for the night so that they won't have to drive drunk. (At least they are being safe.) Also, we all decided we should put money together and get her a more expensive gift rather than lots of little ones. Do I drink? Well yes, sometimes. I drink a little bit of wine or champagne occasionally, but I'm honestly not into the whole "getting really plastered" part of it. Partly because A, I don't really know these friends very well -- and B, my body is really rather adverse to alcohol in large quantities (isn't everyone's?) ... so I really don't want to be a party pooper, but I'd like to drive my own car there and back. I hate being in situations where I cannot find my way out of. If I attend this party and it turns out to be just another masqueraded orgy as has many a party I've attended in the past few yrs, then I'll be wanting to leave immediately. If it turns out that I am comfortable and want to have a drink or two, I will be happy to stay at the motel, but I don't want to be trapped.

And then, they decided they wanted to put all our money together and buy her something from a sex shop.......? Okay, I'm not really a prude, but I don't really want to promote my friends' pre-marital sex lives. Sure, I won't judge what goes on behind closed doors and I'm not an idiot, I know out of a lot of my friends, the only one who isn't having sex, is me -- but that's my choice -- and it's also my choice not to want to contribute to someone else's desires to engage in sexual activity. They can do what they want, without me putting money in ... for what? I am scared to ask. I don't want to know what exactly it is that they plan to buy and I don't want to know exactly what it is they do in their bedroom.

So yep, happy to go to the party -- don't want to go as a group for fear of being trapped, and secondly, don't want to buy a friend a tacky gift from a sex shop -- would prefer to buy her something meaningful. What to do, what to do?