(at around 26 mins) Clay puts one of his missing persons poster on the back of the Escalade and there's a close up shot of the poster as the vehicle drives away from the outpost store. The ensuing shot is of the vehicle entering the city limits of Crystal Lake, passing by the sign, however there's no poster on the back of the vehicle.
(at around 1h 26 mins) The blood and grime on Clay's face in the shed with Whitney, especially the blood on his right cheek, changes between shots.
(at around 1h 5 mins) When Trent and Bree are having sex in the bedroom. Bree is seen sitting up with her hands on top of her head holding her hair. When it cuts to showing Trent's upper body half. You can see Bree's hands by his neck and shoulders. When it cuts back to the same side view as before with Bree sitting on top of Trent as he is laying down. Her hands are all of a sudden back at the top of her head holding her hair. As quick as the shots are shown there is clearly no time for here to get her hands back up that fast.
(at around 38 mins) After the verbal altercation with Trent at the lake house, Jenna leaves with Clay Miller, who is carrying a satchel. As they approach Miller's motorcycle, notice how the position of the satchel changes from being strapped around Miller's left shoulder, to being carried in his right hand, and, finally, back to his left shoulder.
(at around 1h 5 mins) When Jason is walking up to the house and sees Trent and Bree having sex through the bedroom window, you can clearly see the ceiling fan above them is on and spinning. In the next scene which is a close up of Bree from the waist up, the ceiling fan is not moving at all.
(at around 24 mins) It is illegal for patrons to pump their own gas in New Jersey. By law there would have been an attendant on duty and gas would not be paid for inside.
(at around 9 mins) Wade explains that GPS unit works by sending a signal to the satellites which in turn respond; in reality, GPS units only receive signals from various satellites and never transmit any signals.
(at around 26 mins) New Jersey is a "helmet law" state. Clay was not wearing a helmet while riding his motorcycle. A law Officer Bracke apparently chose to overlook.
(at around 11 mins) When the youngman finds the weed plants in the woods, he smells the leaf of a plant. Actually, it's the flower of the plant (the smokeable part) that gives the famous smell, not the leaves.
Near the beginning, as Clay is going door to door, the old lady makes the comment to him that the locals know where to walk to avoid disappearing. A few scenes later, after Clay leaves a barn, the worker inside is killed by Jason. This would be likely outside of Jason's "territory". But the worker had been to the marijuana patch, which Jason considers his territory.
Jason is able to turn the power on and off at the campsite. If the campsite was truly abandoned, all of the utilities (including the electricity) would have been turned off.
(at around 6 mins) You can clearly see two s reflected in the geek's glasses when he looks up during the campfire scene where he tells them about the Camp Crystal Lake murders.