In many episodes, if a character is reading a book it's usually 'A Dinner of Onions,' from the episode "Full Metal Dust Jacket." During a scene in which Bobby is studying for the quiz bowl team, you can see he's watching the directors commentary for 'A Dinner of Onions.'
While watching The Beverly Hillbillies (1962), Hank tells Bobby about "the man who played Jed Clampett and also Barnaby Jones". This of course was Buddy Ebsen, whose final role, before his passing in 2003, was in the Season 3 episode A Fire-fighting We Will Go (1999) as the elderly volunteer fireman Chet Elderson.