When going inside to get the screwdriver to repair the squeaky floorboard it is shown as a Phillips type, when its dropped later on it has changed into a flat-head screwdriver.
(at around 36 mins) When the hero goes looking for the Orc in his house, he's wearing a tank top and no hat. He goes into the basement, and fights the Orc, but now he's wearing a hat and shirt. He kicks the unconscious Orc down the stairs (from the basement to the main floor) and then is back to wearing a tank top and no hat.
During John's first encounter with the orcs, he enters the cabin and gets a Philips head screwdriver, when he falls off the porch, a flat head screwdriver falls to the ground.
Just over half way through, the Special Forces hero is using a .50 cal sniper rifle to take out some of the Orcs, except he is looking through the scope and shooting, but has not removed the lens cap from the far end. It is clearly visibly still on the scope so he couldn't see jack in real life through it.
During the intro scene two Moons are seen in a twilight sky. One is a waxing gibbous (nearly full) Moon being eclipsed by a waning crescent. This would require one moon to be reflecting light from a Sun to the east and the other reflecting light from a Sun to the west. Both Moons should be in the same phase if they are in the same portion of the sky relative to the Sun.