Other mistake: The Duke is picked up in New York. They are headed to L.A. via Chicago. Jack has Eddie wire $500 to Amarillo, Texas. The route from Chicago to L.A. would not take them anywhere near Texas.
Plot hole: At the end of the film Mardukas reveals that he has been wearing a body belt packed with cash - "in the neighbourhood of three hundred thousand dollars" - ever since Jack detained him in New York. Are we to assume that Jack Walsh, an experienced, hard-bitten ex-police officer, now a bounty hunter who routinely chases down violent and armed bail absconders who would kill him without a second thought, didn't even perform a perfunctory search of Mardukas when he detained him? This man used to work for the Mafia! What if he was carrying a weapon? A body belt with three hundred one thousand dollar bills in it would be uncovered by even the most casual pat down.
Jack Walsh: Here come two words for you: shut the fuck up.
More trivia for Midnight Run
Suggested correction: He was using $1000 bills. That's 300 bills in the belt which spread evenly absolutely could have been missed near his waist as part of his clothing.
Rubbish. I specified $1,000 bills as that would be the smallest package he could have secreted about his person, and it would still be instantly detectable. If he used $100 bills the package would be ten times larger, and he would have to carry a rucksack under his shirt.