Hugh Jackman took ice-cold showers every morning of filming in order to help get into character. This tradition started when jumping into the shower at 5 a.m. before realizing there was no hot water. Shocked awake but not wanting to wake his sleeping wife, he gritted his teeth and bore it before realizing that this mindset, wanting to scream and lash out at something, but having to hold it in, was the mentality that Wolverine is in constantly. He then made cold showers his Wolverine preparation routine for each movie featuring the character.
Shortly after accepting the role of Magneto, Sir Ian McKellen was offered the role of Gandalf in The Lord of the Rings, which, originally, he had to decline. He spoke to director Bryan Singer about his interest in making The Lord of the Rings, and Singer agreed to rearrange this movie's shooting schedule so that McKellen would finish his scenes by the end of 1999, freeing him up to travel to New Zealand in January 2000, where The Lord of the Rings had been in production since October 1999.
Neither Sir Patrick Stewart nor Sir Ian McKellen knew how to play chess during filming. A chess master came in to teach them.
To celebrate her last day on-set, Rebecca Romijn brought in a bottle of tequila, which she gave to her fellow cast and crew during a break in filming. Unfortunately, that day she happened to be filming the Wolverine and Mystique fight scene, and she threw up blue-colored vomit (from the chemicals in her make-up) all over Hugh Jackman.
In order to keep her look a secret, Rebecca Romijn had to sit in an isolated, windowless room when not required for shooting: "I had almost no contact with the rest of the cast, it was like I was making a different movie from everyone else. It was hell."
Malcolm Nefsky: (at around 13 mins) After the amateur boxing match in Alberta, the guy behind the man that accuses Wolverine of cheating is Malcolm Nefsky, this movie's Best Boy Grip. Because of the way the scene was filmed, someone was needed to deliver the line, and he was called, because no certified "extra" was nearby.
D.B. Sweeney: (at around 1h 28 mins) The police officer stabbed by Sabertooth in front of the Statue of Liberty. Sweeney is a big fan of the X-Men, and had tried out for the part of Cyclops.
David Hayter: (at around 1h 28 mins) The writer appears as the cop who is kneeling next to Mystique (disguised as a guard, with the hurts caused by Wolverine's blades visible in the stomach), saying that the guard is alive and he must be moved out of there.
Gary Goddard: (at around 43 mins) The director of Masters of the Universe (1987) is one of the men watching Senator Kelly emerge from the ocean (is the man who wears a green plaid shirt in front of two boys). Singer and Goddard are good friends, and before production, Singer sought out Goddard's advice on directing "a comic book movie".
Cal Dodd: The actor who voiced Wolverine in X-Men (1992), can be seen on the right hand side of the screen as Senator Kelly exits the water.