The extra (wearing a striped shirt) behind the limo driver at the airport is not using coins while supposedly playing the slot machine (he is, apparently, an unauthorized extra that snuck onto the set).
When the Griswold family is playing Keno, The #80 comes up on the Keno board. The next time the Keno board is shown the #80 is not on the Keno board, then it comes up again in the following scene.
Rusty claims he put a dollar in each of the slot machines to get a car - however the amount was never a dollar. In the first car win scene, he uses a quarter. In the second scene he uses two quarters.
The spaghetti on Ellen's dress disappears between shots just after entering Rusty's suite during a party.
When Rusty won his first car, he put one coin into the slot machine. Winning the car required three coins.
When Clark is at the Blackjack table and bets $1,500, he places it in the dealer's hand. No dealer in any casino is allowed to take money out of a player's hand. It must be placed on the table.
On the multiple occasions that Marty revealed a Blackjack (21) with the ace being the visible card, he hadn't offered Clark insurance, which is what a dealer is supposed do do when they are showing an ace.
When Clark is shooting craps and he gets a 7 on the Come Out Roll, the dealer should have collected all the of the losing bets in the "Come" area of each number but he does not.
The children's card game of War is depicted as some demented underground game of chance. It had been patented as a real casino game in 1993 and been played in northern Nevada casinos starting in 1994.
When The Griswalds are playing Keno near the end, only ten numbers were called. Regardless of how many numbers a player picks or is allowed to, 20 numbers are always called in Keno. As it is played in the movie, the odds of winning this game would be astronomically worse than winning the lottery.
When Clarke is driving the hijacked tour bus through the wall at Wayne Newton's house, you can see damage to the front of the van before it crashes through the wall.
When the family arrives at the Hoover Dam, Cousin Catherine says she loves electricity, and that Eddie has said they will get it soon. However, earlier in the film when Ellen and Catherine were in the kitchenette of the trailer, Ellen opens the fridge door, and the light is on, so it is powered. Perhaps by a generator, but it's still electricity.
When Clark is standing outside the lavatory doors on the plane prior to attempting to "join the mile high club", there are clearly only a few inches between the three doors. When he finally steps inside the center lavatory with Ellen, there is obviously at least a foot between the edge of the door and the wall.
When the tour bus crashes into Wayne Newton's house you can see that it's not Clark driving the bus nor Eddie sitting next to him.
When Clark is missing during the Siegfried and Roy show, Rusty and Ellen have a brief exchange where neither one's lips move.
When the Griswolds leave for Hoover, Clark tells Cousin Eddie that Rusty is sick and his mouth does not move.
When Clark is onstage with Siegfried and Roy, his words do not match his lips.
Reflected in both vehicles when the Griswolds are driving alongside the girl in the Ferrari.
Reflected in the passenger door of the taxi that takes Ellen to Wayne Newton's house
Yellow blocking tape visible on the sidewalk when Rusty returns to the Fake I.D. Salesman.
Reflected in the mirror when Clark is talking to his wife about baccarat in the hotel room.
The Reflected in the chrome of the Griswold limousine when they are driving down the strip.
The club Vicki is a dancer at has an address on Las Vegas Blvd (AKA The Strip) according to the taxi cab ads. However, when they emerge from the club, they are standing across the street from the Hard Rock Cafe. There was only one Hard Rock Cafe in Las Vegas in 1996/1997, and it is at the intersection of Paradise/Harmon, which is actually about a mile east of Las Vegas Blvd.
When Rusty if having his picture taken for the fake I.D., the Zip Code (85737) is not for Yuma Arizona, but for Tucson Arizona.
Cousin Eddie said he got a huge plot of land just North of Las Vegas, but his trailer is actually in Jean, NV which is South of Las Vegas.
While Clark is driving home in his Expedition, he passes his house and his neighbors Margo and Todd's house several times before sliding in his driveway.
The road the family members are seen driving down at the end of the film is Interstate 15, which would take them to California, completely the opposite direction of Chicago, as the superimposed road sign states. (On an unrelated note, if they had continued going down this road, they would eventually get to Baker, California, which is the site of the "World Largest Thermometer" mentioned by Audrey earlier in the film.)
The fact that Clark lost nearly 22,000 dollars gambling wasn't nearly as dramatic as it had to be. In reality Clark could have sold any one of the cars that Rusty had won which would of recouped all of the money he lost if not more.
After Audrey exits limo,u can clearly see a very red(unrealistic version of wound from sunroof mishap),going across her abdomen but you see none across her backside.