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: 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: 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: 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)
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.