In the original story ("Paycheck" by Philip K. Dick) Jennings sends to himself very different items, and there were only seven of them. They were: "A code key. A ticket stub. A parcel receipt. A length of fine wire. Half a poker chip, broken across. A green strip of cloth. A bus token."
John Woo originally did not want to do his trademark "Mexican Standoff" in this film, but Ben Affleck begged Woo to include the scene, having been a big fan of Woo's films The Killer (1989) and Hard Boiled (1992).
Just before Michael starts his second project, he comments on the Red Sox making the World Series. Although this film was released in 2003, it is set in 2004, and accurately predicts the Red Sox making the World Series, although it incorrectly predicts that they would lose.
Among the alternate features in the DVD, is the final, wherein after Michael and Rachel get away, they pass by a pawn shop, and Michael sees the ring that the kid took off him on the bus. He gets it, and gives it to Rachel.
In the DVD special feature about the film's stunts, Stunt Coordinator Gregg Smrz explains that in a chase-scene crash between a car and a big rig truck, the truck was actually towing the car by use of a cable system that the special effects department fabricated. One of the chains connecting the two vehicles is noticeable during this crash sequence in the film.
The twenty items that Jennings sent to himself are: sunglasses, pack of cigarettes, bus pass, diamond ring, paperclip, fortune from a cookie, janitor's key, lighter, hairspray, matchbook, Allcom pass, BMW key, looking glass, stamp, ball bearings, allen wrench, half dollar, cross word puzzle, bullet, and a watch.
In the "Making of" featurette on the DVD, John Woo says that the visual similarities in the lead character to Roger Thornhill from North by Northwest (1959), as well as similarities in chase scenes, et cetera, are there on purpose.
Most of the main cast have portrayed characters from various versions of the Batman universe. Ben Affleck played Batman, a.k.a. Bruce Wayne, in Batman v Superman: Dawn of Justice (2016) and Suicide Squad (2016). Aaron Eckhart played Harvey Dent, a.k.a. Two Face, in The Dark Knight (2008). Uma Thurman played Dr. Pamela Isley, a.k.a. Poison Ivy in Batman & Robin (1997). Michael C. Hall was the voice of Kirk Langstrom, a.k.a. Man-Bat in the animated movie Justice League: Gods and Monsters (2015). Colm Feore played Dr. Francis Dulmacher, a.k.a. Dollmaker, in the Gotham (2014), and Joe Morton played Dr. Silas Stone in Batman v Superman: Dawn of Justice (2016).
One of the items in the envelope is Michael's identification card from Alcom Corporation. In an F.B.I. office scene, there is a close shot of the card with a U.P.C. barcode 071486036043. This code corresponds to Premiere Magazine published by Curtis Circulation Company.
The sender address of the envelope is M. Jennings/Alcom Eng. Dept., Discovery Park, Orondo, WA 98830, phone 206-555-0101, and the destination Jane Anderson/Reddy Grant, 401 Burrard St., Seattle, WA 98817, phone 206-555-0199. The shipping date is 5/20/07.
The trivia items below may give away important plot points.
Thought up as a joke by a Visual Effects Engineer (according to the "Making of" featurette on DVD), some scenes make hints that the machine may be a sophisticated hand-lines reader. Before Michael goes to Allcom for his job, he's getting inspiration from a ceramic hand sculpture, showing the lines. When, at the end of the film, he uses the machine, there is a close shot of interaction between the machine and his hand-lines.
DIRECTOR TRADEMARK (John Woo): (birdcage): In the final scene, Michael finds a winning lottery ticket hidden under newspaper in the bottom of a birdcage. This is similar to the opening scene of Hard Boiled (1992), where gang members sell illegal firearms in a tea house, by concealing them in the hollow bottoms of birdcages.