Important person, as in big cheese. Also: big kahuna, top dog.

Also outdated slang for doing whatever is necessary to cover your ass when the police arrives. Cheese it can be interpreted as: watch out, run away, hide your illegal substance, hide yourself, etc. Prominently (and ironically) featured in Bringing Up Baby -- Katharine Hepburn says Cheese it, the Fuzz while already in jail -- and assorted 1930s gangster movies.