When Felix is in the Cadillac in the garage the car has a TV antenna on the trunk. When the car goes through the wall of the garage, it's missing the antenna and indeed is a different (fewer options) model of Cadillac.
After Babs (Rosanna Arquette) goes out onto Felix's deck to sunbath, her character disappears from the film for 30 minutes before reappearing by Lila's side to hitchhike back into town.
When Gary is serving coffee at Sally's house while her participation in the new film is being debated, he picks up the silver coffeepot twice between shots.
One shot of the dead Felix gripping onto a fishing pole shows him slightly moving.
When Felix is shot trying to steal the Night Tide negative, the reels of film that fall out of the cans are a positive element, not a negative.
When the nurse enters the hospital room to give Polly Reed a shot, something falls off the tray she's carrying.
When Felix Farmer re-encounters Harrigan, now working as a security guard at a film lab, he tells Harrigan he's "late for a very important date," to which Harrigan replies, "Oh, like 'Alice in Wonderland' ... the March Hare!" Actually, it was the White Rabbit (specifically, in Disney's movie version) that was "late for a very important date," not the March Hare.