Plot hole: How did Kincaid get a picture of Sid from the Delta Lambda Zeta mixer in part 2? No one took any pictures of her. Aside from that, anyone who's seen pictures Neve Campbell online will know that that's a publicity shot from Scream 2 rather than something intended to be a "real" photo.
Plot hole: It has already been mentioned that a certain shot reveals that Sidney isn't wearing the bullet-proof vest when she should be. Further to this, most of the shots in the climax sequence make it impossible for her to be wearing one, as you can see the contours of her chest throughout. A bullet-proof vest would flatten the appearance of this.