In one scene, Sonny goes to kick start his Sportster. He forgot he'd left it in gear. Had the bike started, it would have shot out from under him.
During the fight outside the Hell's Angels' Club house, one of the bikers is thrown on the roof of the car and a cameraman is visible in the back seat.
In the casino a crewmember's hand can clearly be seen throwing the coins into the bottom of the machine.
When the Hells Angels are chasing Chuck through the desert the shadow of the helicopter filming the scene is noticeable.