The leaf on Inez Wong's hat is supposedly a marijuana leaf. This refers back to Leela's quote in Mars University (1999): "They planted traditional college foliage; ivy, trees, hemp. Soon the whole planet was terraformed."
Zapp throws an empty Slurm can on the ground at the feet of a Native Martian, who sheds a tear. This is a reference to the famous anti-littering commercial Keep America Beautiful: The Crying Indian (1971).
The underground Martian settlement is visually based on Mesa Verde, the ancient cliff city built by the Anasazi tribe in Colorado.
The Wongs claim they own the "whole western hemisphere" at 17.9 billion acres. Mars has a surface area of 144.8 million km². In acres that's 35780859236.4 acres. Half of that is 17890429618.2, or 17.89 billion.
Sitting around the campfire, Bender tells a literal "ghost" story about a computer screen that, despite being unplugged, still showed the Windows logo. The after-image that remains briefly on the screen when a computer or television is turned is off is referred to as a "ghost image."