When young Brian is teaching young Jake the correct way to do the sign of the cross we see Brian consistent making the correct cross but Jake make several incorrect shapes with that last being a famous self-portrait of John Lennon.
While they are driving back from the airport, reminiscing about old school classmates, Brian says, "Remember Aaron Portnoy? He complained a lot." That's a reference to Philip Roth's novel, "Portnoy's Complaint."
There is a scene about the middle of the movie in which Rabbi Jake brings in a gospel choir to liven his service. As he urges the congregation to join in he shouts "come on, all the young Jews!" He is playing with a cherished, "mondegreen" - an often misused, misheard lyric - of David Bowie's and the Mott Hoople's "All the Young Dudes". The "misheard" words were sung regularly at fraternity and college parties throughout the '70s.