When Alan stays with Vic after Vic's leg is broken, Vic also has a nasty cut on his left cheek, with blood appearing to coagulate. Shortly afterwards, before Alan takes Vic down the river, there is no sign the cut ever existed.
When Vic is showing the slide show to Alan's parents in the beginning, you can hear him say the same thing twice. "We caught this fish on the first day, This is where we camped the first night".
After Vic is injured, Alan and Vic go to sleep above the river canyon. They wake up in camp next to the river the next morning.
At the end of the movie, the paddle handle changes from a tapered handle to a T-grip.
Alan's sitting position changes while watching Vic catch a fish.
On the evening of the first night's campout, Vic points out the constellation Orion low in the sky and tells a story relating to it. However Orion is not visible in late summer at the latitude they were supposed be at until early morning, around 4 am.
When the boys are all urinating, no urine is seen at all, not even at the angle where urine should have been seen.
Reflection of camera crew visible in Mitch's helmet when crossing the bridge.
When the boys first leave Vic behind, they stop for the night with no tents and curl up because they're cold. Although Alan is carrying a perfectly good sleeping bag, he uses it as a pillow instead of using it to keep warm.