The music heard during the chase sequence on top of the train was featured on the album "The Carl Stalling Project: Music From Warner Bros. Cartoons 1936-1958". It is part of the "Various Cues From Bugs Bunny Films" track.
The hobos are modeled after "The Honeymooners" characters Ed Norton and Ralph Kramden.
When the bums exclaim "It's fooood!", their mouths take the shape of the letters in the word. This is likely a reference to a Ford TV commercial from this time period, where a character would exclaim "It's Foooord!" and his mouth spelled out Ford.
Bugs makes a reference to the smog Los Angeles was already experiencing at the time, and pronounces it "Los An-guh-leese." Probably some Termite Terrace humor.
As the train enters the tunnel, lettering can be seen on the cars. The red car reads SERVES OUTER SPACE and the yellow car reads DON FOSTER FRUIT EXPRESS. Don Foster was a longtime Warner Brothers animator.