(at around 22 mins) At one point Sarge Crockett smashes out one of the windows in the armored truck with the butt of a rifle. In reality, that is impossible since the polycarbonate "bullet-resistant" windows would not be penetrated even by a bullet, much less the blunt plastic butt of a rifle.
(at around 28 mins) When Francisco is swimming to the ferry you can see the actors scuba mask on the zombie he bites the finger off of.
During the climax zombie shootout scene, Muldoon remarks that he has one bullet left. When he then proceeds to shoot the bullet at the antagonist, he fires twice, sending not one but two bullets hitting him.
The soldiers are driving around in jeeps at the start of the film, most of these were retired in the 1990s. By the late 2000s, they had been replaced with Humvees.
The soldiers are all wearing woodland-camouflaged BDUs; by the late 2000s these were all replaced with the universal-camouflage ACU.
(at around 21 mins) In the back of the armored car when the boy shows the soldiers the video on his iPhone the cellular carrier name on the screen says "Rogers" which is a Canadian company. The movie was filmed in the Toronto area but the story at that point takes place in Pennsylvania where AT&T would have been the cellular carrier for the iPhone.