When Barbara is speaking to the school nurse, you can see the door behind the nurse has a pocket on it with a black magazine/book sitting in front of a Manila folder/envelope. Towards the end of their conversation, before standing up, the black book/magazine disappears, and there is only the Manila folder/envelope.
Martina is asked to bring her grandma laxatives. She only grabs her keys and leaves the box of laxatives on the drawer, but when she and her friends dump the deer a little while later she pulls the box out of her jacket pocket.
During the final chase scene Martina and Dawson enter the room where Boner supposedly lies dead on the bed. The exit door is closed. After a reaction shot of Martina and Dawson the cut-back to scene now shows the door open and Martina and Dawson escape through it.
At one point in the movie, Boner says, "Roofies are bull. I take them before every date, and I never get laid." If Boner actually did take roofies before every date, he could have gotten laid on every single date and not remembered since roofies make you forget what happened whenever you took them.