The 'particle gun' that Phoenix picks up in the museum is actually a prototype of the real-life Heckler&Koch G11 rifle, the first gun ever to fire caseless ammunition. The gun and its ammo were developed in the Cold War to save the expenses for the cartridge case production. It was tested and modified for field use, but with the collapse of the Soviet state (which ended the Cold War) in 1991, the production program was cancelled.
After Simon Phoenix kills Warden William Smithers, Huxley tells the computer to display a list of parole hearings for the day. One of the names that is stated and printed on the screen is Peterson, Scott. A man called Scott Peterson was convicted of murdering his wife and unborn son in 2002, 9 years after this movie was made.
Demolition Man contains several references to the novel "Brave New World" by Aldous Huxley. Sandra Bullock's character's name is Lenina Huxley, from Lenina Crowne, a main character in the book, and the author's name. Sylvester Stallone's character is also named for a character in Brave New World, John the Savage.