When Natalie, Zach, and Tommy are at the gas station, a collection jar with a sign that says "Please Help Find Stewart Fund" is attached to the pillar holding up the cigarette rack. When they leave, the jar and sign are attached to the cash register on the opposite side of the counter.
Since many people in emergency situations can't talk, 911 operators don't hang up if there is no answer on the other end. The operator stays on the line to trace the call, dispatch emergency vehicles, and await any possible changes.
After the car accident, Zack tells Natalie that he didn't know about the baggie of coke that Brad had. In fact, there's no indication that he knew about it either before or after the crash; the baggie is discovered by the cops when the kids' souls aren't around.
The goof item below may give away important plot points.
Dave gives Zack a couple of soul-taking rings so he can try to save Natalie. Handing Zack the soul-taking rings should capture his soul, since this is what happens to everyone else when the rings touch them.