Henry Rollins had his huge sun tattoo covered up for this role.
After Jack punches Gary in the bar fight scene at 1h 24m, he looks at his fist and notices a tooth is embedded in his knuckle. This actually happened to Henry Rollins while he was touring with the Rollins Band in Australia. Rollins admits he lost his temper and punched a man in the crowd that was disrupting his performance. Henry left the wound as it was. It later became infected to the point of requiring surgery because the wound was septic, almost costing Henry his entire hand.
The bar where he looks for Andrea is called the Bovine Sex Club in Toronto.
The coat Jack wears throughout is an American Eagle brand jacket.