The tunnel to Toontown is the same tunnel director Robert Zemeckis would later use in Back to the Future Part II, which came out the following year in 1989.
There's also a photo of Eddie and his brother as kids working as circus clowns — this setup pays off at the end of the film when Eddie uses his old clowning ~skills~ to distract the weasels.
The Dip ingredients used to kill toons is a mix of turpentine, acetone, and benzene which are actual paint thinners — so, the Dip LITERALLY erases animated characters! :-(
And the shoe that gets "dipped" was voiced by Nancy Cartwright (aka Bart Simpson!) — although, she went uncredited.
And there's a sock and buskin (comedy and tragedy masks) symbol made from Felix the Cat's face above the tunnel entrance.
Eddie's toon gun comes in a box inscribed by Yosemite Sam that reads, "Thanks for getting me out of the Hoosegow."
The truck Eddie crashed into in Towntown says, "Acme Overused Gags" and carried things like bowling balls, bananas, and a piano.
Also, there's a salon for HARE cuts in the background here with the image of a hare about to be decapitated.
There's a message written on the men's room wall that Eddie hides in that says, "For a good time call Allyson 'Wonderland' — the best is yet to be."