When questioning Rudy about his true identity, and how much he knows about Ashley's background, Gabriel puts a Glock to Rudy's head. Upon doing so, it sounds like a hammer cocking back on the pistol. Glock pistols do not have hammers.
In the first scene at the Tomahawk Casino, "Nick" bumps into a waitress and she drops the drink she's carrying. A glass breaking sound is heard. Also when one of the characters discovers that there was no remodel done on the Tomahawk - he runs off, dropping his glass - and the sound is heard again. There is carpet visible, throughout the Tomahawk which would make such a glass breaking sound impossible.
Monster throws a dart into the front of Rudy's shoulder, but in the next shot it is stuck in the back of his shoulder (shots of additional darts being thrown were cut from the final version so we never see this one land).
When Rudy is pointing the water pistol at one of the gang members, at one angle, his arm is fully extended. At a different angle, his elbow is bent so we can see the gun as his face in the same shot. When they cut back and forth, Rudy's arm jumps from extended to bent and back.
While escaping across the ice alone, Rudy gets shot at, and despite being in the middle of a frozen lake, with nothing for a distance on either side, a bullet ricocheting off metal can be heard right next to him.
When the gang initially robs the casino, they are telling the security guards to drop their guns. One of the guards has the gun up and ready, but the slide is obviously back. There is no way the security guard could have shot the gun with his gun not ready.
The goof item below may give away important plot points.
Rudy starts the car as it rolls out of the trailer, then he makes his comment to Nick about "Never putting a car thief...", as he talks, he hits the cars gearshift lever downward. This would put the car into "Drive", but the next shot shows the car going into reverse to hit Nick.