When Porter sits on the sidewalk to wait for Rosie, the blue backpack is about a foot behind him. Although Porter later says "Backpack, backpack," and Rosie replies, "Got it," when Rosie first comes around the car, the backpack is nowhere to be seen.
When Porter and Val run their Nova into the Chows' car, although the cars have impacted and come to a dead stop, the reaction shot of Porter and Val shows buildings still moving past the side windows. Also, Porter's head has snapped forward all the way to the steering wheel before Val even reacts to the crash.
When the Chows crash into Porter on his way to meet Val for the $70,000, the windshield is seen completely smashed in. In subsequent shots the windshield is significantly less damaged.