In the first classroom scene, Mr. Thorn is writing rules on the blackboard, and at the bottom it says, "No Slackers." Mr. Thorn is played by James Tolkan, who played Mr. Strickland in the "Back to the Future" series, and was fond of calling both Marty and his father slackers.
When Mrs. Dumore sees Ben in the bank, she says she plans to make him "Hubbie #7" and a bunch of pictures are shown of her previous husbands. Her other husbands are John Ritter in several costumes.
Big Ben says that he only sold one starter kit. If you look very closely, you'll notice he sold it to Voytek Claukinski.
The only actor to appear in all three films and the short-lived cartoon series was Gilbert Gottfried. Jack Warden appeared in all three films, but not the cartoon.