In Mike's reference to "The Wizard of OZ" in which he asks "Wicked Witch of the West, Wicked Witch of the East, which one was bad?" And Heather answers "Wicked Witch of the West was the bad one" Actually both Witches were bad. The Witch of the North was the good one.
After the map is lost, there is much talk of following a single direction in the hope of getting out of the woods ASAP. The most obvious course of action (which occurs, apparently, to no-one) would be to follow the course of the river that they keep crossing then hiking away from.
When Josh goes missing and the two others are calling his name, Mike is wearing a plaid shirt with a white t-shirt underneath. When they change views his t-shirt is black. When they cut back it's white again.
When Mike is trying to convince Heather to let Josh relax for a few minutes without being bothered, it is revealed that the group has completely run out of cigarettes. Not long after this scene, we see Mike and Heather sitting down smoking together.
The goof item below may give away important plot points.
Incorrectly regarded as goofs
While Rustin Parr's house was said to be burned down (notably in Curse of the Blair Witch), we see it and go inside. But this is probably a supernatural phenomenon of some sort - possibly a time warp; it explains, in part, why the filmmakers were never found.