When Charles and Lulu start making love in the motel, Charles's lipstick smear on the upper lip first moves from right to left, then disappears and reappears (on the left).
After Lulu offers Charlie a ride at the beginning of the movie and they approach her car, parked on the street, Lulu tosses both her bag (purse) and the portable cassette player into the backseat of the car through the driver side window and is not carrying anything on her shoulders when she gets into the car. In the next shot, when Lulu is in the driver seat, the cassette player is still hanging on her left shoulder, and she puts it in the backseat a second time.
In the motel scene where Ray throws Audrey into the pool, she goes in with socks and sneakers on. Next shot shows her swimming out barefoot.
In the motel scene, Charlie - while removing his blue dress shirt - pulls it over his left shoulder twice.
When Charlie Driggs pulls into the gas station and is first talking to the attendant, we see the Civil War re-enactor and the other station employee walk by twice in the same direction.
Beer is purchased in a convenience store in Pennsylvania (a PA Lottery sticker is on the door). Beer cannot be purchased in convenience stores in PA.
Early in the film Charlie and Audrey drive over the New Jersey-Pennsylvania state line. They drive over land, but that's not possible. They would have to cross over the Delaware River on a bridge; from north to south the state line is in the middle of the river.
When Charlie finds newspaper clippings tucked into Audrey's yearbook, one article has the headline, "Quincy man arrested: charged with convenience store robbery," and another article has a related headline: "Additional stickup's [sic] attribute to Quincy 'hit and fly' gunman." This is obviously foreshadowing about Ray - but if you read the body of both articles, they're really irrelevant reports about foreign policy, mentioning Libya, NATO, the Pentagon, U.S. Secretary of State George Shultz, etc.
Lulu's drink of choice is Seagram's 7, an American blended whiskey. When she enters the package store, she specifically asks for 4 pints of Scotch, and the clerk retrieves the Seagram's from the shelf.
When Charlie finds Audrey's yearbook, her name is spelled "Audry Hankel" (without the "e" in her first name that's seen in the credits), and her photo doesn't plausibly look like a young Audrey.