The car mechanic in "Road Trip" is a reference to Billy Bob Thornton's character in the 1996 movie Slingblade.
When Arnold and Grandpa go to the movies the screen shows a famous scene from Harold Lloyd's 1923 film "Safety Last!".
When Grandpa is going over his will a Chinese checkers board makes an appearance. In an earlier episode, Grandpa played Chinese checkers professionally.
As of this episode, Arnold's grandpa Phil, never passed away.