Continuity mistake: When Trent and Bree are having sex, the ceiling fan is on then off.
Continuity mistake: When Clay and Jenna leave the lodge and walk over to his motorbike Clay has his bag on his left shoulder. In the next shot it is instantly in his right hand. Then when he sits on the bike the bag is still in his hand, but in the very next shot it's suddenly back on his shoulder. (00:37:55)
Continuity mistake: When Chewie is getting killed, Jason shoves the screwdriver in the middle of his throat. Then it's suddenly to the side, facing away from the camera. (01:04:56)
Continuity mistake: Jason kills Bree and her eyes are closed. When he throws her out the window and she lands on the car, they are open. (01:19:15 - 01:22:05)
Continuity mistake: Clay puts a 'Have you seen Whitney' flyer on the back of the SUV. When the car drives past the Crystal Lake sign, it isn't there. When it parks, the flyer has returned and a guy removes it in anger. (00:24:35)
Continuity mistake: Near the end when Jason is fighting with Clay in the barn, Clay's face is relatively dirty and sweaty. But in the shots when Jason is trying to force Clay's face into the rotating blades, his face is very clean and dry. Then in following shots it is dirty and bloodied up again. The cleanliness of his face does differ through the whole scene.
Continuity mistake: When Bree spins around and shoots at Clay with her camcorder as he enters the lodge, the position of her fingers on the camcorder display lens differs between each shot. (00:36:35)
Continuity mistake: When Clay and Jenna are at the camp and are about to leave, but Clay's flashlight runs out of batteries, he digs into his bag to get more, but they spot Jason so he leaves the bag and hides. Jason finds the bag and takes it with him. When they're leaving the camp, Clay's flashlight is working again.
Continuity mistake: After Chewie takes a drink from the bottle in the tool shed, he looks at it holding it in his left hand. There is then a cut, and suddenly he's leaning against the fridge with his left hand now holding the bottle in his right. (01:00:02)
Continuity mistake: When Lawrence is killed, Jason throws him onto the pile of logs, and the axe sticks through his chest. The angle of the axe is running down his back, but when we see Lawrence in the spa the axe is in a different angle.
Continuity mistake: The shoe changes positions in the "shoot the boot" scene, from toe to his mouth, to heel to his mouth.
Continuity mistake: When the log shredder starts looking at a copy of "Hustler", he opens it up so a three-fold picture is revealed. But several seconds later, when he starts to lick the magazine, the third fold out disappears and the magazine only is open to two pages.
Chosen answer: When Jason brought her brother's backpack, you can see a small table next to the mattress with some bottles and cans, there is also something what looks like bag of chips (or maybe marshmallows?). I'm sure that he knew that she needs food, and brought her something from campers or cabins.