Plot hole: Stewie gets out of the car seat and goes back to bed, leaving the blanket at the bottom of the seat. When they get to New York, Lois goes to get him out and realises he's gone. But when they started the trip the blanket was covering the entire seat to make it look like Stewie was still in it. So who ever "covered" him up knew he wasn't in the seat before they set off.
Continuity mistake: Toward the end of this episode, Stewie is at home in the living room talking to Rupert about how depressed he is about being alone. All of a sudden he hears his family come back home, so he gets up from the couch and runs to the window leaving Rupert on the couch. As soon as Stewie moves his head away from the window take notice that Rupert is no longer on the couch.