I think you can get at least get drunk for sure.. I read in an article that there is a drunk driving mission..
It blurs your screen up and makes all the directions on the stick actually got to random directions, so you are all over the road and shit.
I'm pretty sure, there's a good bar scene in this game, and there'll be a lot of interactivity and shit in them.
I've seen at least two different enterable bars on the GTA4 page.