Benson is referring to the movie Primer in regards to his business attire costume.
Eileen's costume is a reference to Samus, star of the Metroid series.
Mordecai and Rigby are dressed up as Kaneda and Tetsuo from the Manga/Anime Akira
In the "King-Sized Candy Bars" segment, Eileen and Rigby's costumes are references to Captain Kathryn Janeway and Commander Chakotay from Star Trek: Voyager (1995).
Hi five ghost has morphed into the shape of E.T.'s head, compete with the glowing finger.