In the pilot episode, a yellow beetle car drives by. This is Emma Swan's car on Once Upon a Time. In the episode "Heart of the Matter", a black Mercedes drives by which is Regina Mills' car on Once Upon a Time.
The characters Robin Hood, Maleficent, Little John, Will Scarlet, Cora, Ashley Boydd (Cinderella) and Leroy (Grumpy) are in once upon a time and once upon a time in wonderland.
The Jabberwocky is not the name of the monster in Lewis Carroll's sequel to Alice's Adventures in Wonderland (Through the Looking Glass.) The monster itself is actually called just the Jabberwock.