During "The Crate", when Wilma is making a fool of herself at the luncheon, she says the line "Whoever that etiquette crotch is." Not only does the line barely match the movement of her lips, the line is said in a voice that doesn't quite match Adrienne Barbeau's. Internet research reveals the original line was "Whoever that etiquette c**t is," but was changed in post-production at the request of Warner Bros.
As Richard hurriedly drives his Jeep away from Harry's buried head, the back window is swung up. With the tide quickly coming in, he must hurry. As Richard approaches his house, the window is down. On this model of Jeep, the spare tire must be swung away from the window in order to close it.
In the segment "Father's Day" - which purportedly takes place on Father's Day (which is in June) - it is already completely dark outside by 7pm. By this time in June it wouldn't be completely dark outside until much later in the evening.
In "They're Creeping Up On You," Upson Pratt smashes a cockroach with the butt of his gloved fist (in a close-up), and in the next shot his white glove is clean as he looks at it. If he is imagining the roaches, as the movie implies, the glove would be clean.
The goof item below may give away important plot points.
Near the end of the "Father's Day" story, Sylvia gets impatient and goes to the kitchen calling to Mrs. Danvers. She sees the muddy footprints and investigates further. Mrs. Danvers' corpse falls against the back of the kitchen door with her face in the round window. As Sylvia lets go of the door, you can see the dead Mrs. Danvers blink as she slides across the window out of view.