Following security policies
I just heard an interesting story that may show why having checklists for security isn't quite as good as having people use their good judgment to carry out the intent of security policies. This story concerned the way in which the TSA apparently inspected a traveler's luggage.
The storyteller's wife was recently flying from Albuquerque to San Jose. Knowing that the TSA randomly inspects luggage, she didn't lock the bags shut. Instead, she fastened the lock that came with her bag to one of the pull tabs of the zipper. This didn't stop the zipper from functioning, of course. To lock a bag shut you need to run the lock through two pull tabs. A lock on a single pull tab just makes a fancier pull tab and doesn't actually stop anyone from getting into your luggage.
When she got home, she noticed that the pull tabs of the bag had been torn from the bag, which contained a note from the TSA explaining how they had opened her bag for inspection. Apparently, the TSA just rips off any locks on luggage, even if they're not actually locking anything shut, and it doesn't leave it to the judgment of an individual TSA employee to decide whether or not a particular lock actually needs to be ripped off.