In the river scene when they encounter a "looker" in the water, Malorie's pistol was taken in the struggle and she is left with only the machete to attack with. The pistol appears to be dropped in the water, yet when scavenging for blankets and food, Malorie has the pistol again.
After Malorie and Jessica crash the car, Malorie gets out, looks at the blood on her hands, and walks to the house. In the next scene, her hands are clean.
Malorie warns the kids about the dangers ahead just before the boat hits the rapids. Under the blanket, Girl's blindfold moves from her forehead to her neck, and back, between shots.
The high-heeled shoe Lydia kicks off while running down the steps goes from lying on the second step to lying on the fourth step to lying on the second step again, to lying on the seventh step to completely disappear from the steps without anybody touching it.
The eyes of people who become suicidal after seeing the supernatural force become darkened. The eyes of the woman in the hospital hallway banging her head on the glass are unchanged (at 10:07).
Small hand-held radios and even larger sets as used need repeater stations to transmit and receive more than a few kilometers. These are unlikely to be functioning after five years.
The electrical grid appears to be intact, even though most of humanity no longer exists. Electricity can be generated without much human intervention. The Hoover Dam can operate for up to 2 years without human intervention.
Cell phones, televisions, and communication systems stop working the first day Malorie enters the home, but the car's GPS works days later. Cell phones have a range of up to 40 miles, and require towers. Televisions require either a physical cable or a local broadcast tower, either of which could lose power or be turned off. GPS uses satellites 12,000 miles above the earth, sending radio waves that cover the planet. Standalone GPS devices existed before the invention of smartphones. The satellites would need continuous control (currently from Schriever Air Force Base in Colorado, or Vandenberg Air Force Base in California) but it would likely be maintained as a priority by any working remnant of the US Air Force.
It is not explained why those in the supermarket didn't just return to the house and bring the others after coming up with the idea to live there. - Because of the 'people' living in the freezer.
There is absolutely no reason why Malorie wouldn't also plug her children's ears to lessen the impact of the voices.
Jeep Grand Cherokee proximity sensors don't cover all sides of the vehicle, just front and rear. The screen shows yellow and red, not green.
When they arrive back from the mall (51:56) and see the house from outside, newspapers are plastered on the outside of some windows on the 2nd floor, while the windows next to it have newspapers inside the glass.
When two injured characters are fighting over a pump-action shotgun, the scene cuts to Malorie listening to them from another room. Two gunshots follow, and the second is too soon after the first for the gun to have been pumped.
The car's proximity system did not detect the curb that Tom hit right at the start of the drive.
When the group decide to drive the car to the supermarket. They painting only one of the windows on the car, and tapes old newspapers on the other windows, instead of painting them.
Douglas pours Malorie a glass of whiskey saying "... a quarter ounce of whiskey isn't going to tip the scales." The drink he pours is at least 4 ounces of whiskey.
When Malorie cycles the pump-action shotgun, it makes the sound of empty shells hitting the floor, not the live rounds that would make a heavier thud.
The tires of the two gray sedans squeal when making the loop at the end of the gravel driveway.
Given that the river floor contains so many jagged rock protrusions and the water is so choppy, there is only a very small chance that three people would overturn and actually make it out with no loss of life or major injuries.
The rapids of the river Malorie, Boy and Girl are trying to cross were mentioned to be very dangerous to cross on a boat. Given the group finds the place they're looking for right after the rapids, there's no reason why they couldn't moor the boat before the rapids and go to the destination on feet without risking their lives.
At the end of the movie in the atrium, it is revealed that birds warn of the approach of the supernatural entities. That being the case, Malorie and company could have taken the birds in a cage with them anytime they went outside and put on blindfolds only once the birds became agitated.
Modern gasoline contains ethanol and without proper storage it starts to deteriorate after a few months. It is unlikely the roaming bandits would find usable fuel for their vehicles.
In reality, someone would have stayed with Greg to try to prevent him committing suicide if necessary.
When Tom is about to let Olympia in, he insists she put up a blanket so that his view will be blocked, but there's obviously no reason why Tom would have to look outside just to open the door.