When Sam and Gus are getting a drink of water at the first creek, the bottoms of Sam's jeans are already wet, probably due to multiple takes.
After being so long in the wilderness Sam's hair would've grown a lot longer.
Strangely, whenever Sam builds a campfire from wood there is no smoke. That would be impossible. They were probably using propane burners hidden in the ground of the campfire circle.
When Sam is chopping out the tree for his house, the sound of the axe hitting the wood doesn't match that of it actually hitting the tree.
When Sam is taking Gus out of his box for the first time, he should not have left it in the wilderness. A naturalist would be concerned about trash being left behind and taken it with him, empty.