When Stanley is shot with the paint balls, they first hit him just above his waist, then, later in the film they are higher up his chest.
After Stanley rips open Kate's shirt with a knife, in the next scene she is seen running through the forest and her shirt is buttoned again.
After Zack, Kate Riff, Vicky and Ashley leave the gas station, Zack is lighting up a joint with a green lighter. When the camera switches to a different angle, he's now holding a yellow lighter. When the camera switches back to the previous angle, the lighter is green again.
When Stanley is standing beside Zack as Zack is being burned alive, you can clearly see the arm of a crew member in the background.