Blackhorse6 - I got up close and personal with the Utility Duffel today, cool bag. I really don't think you're going to have a problem with keeping things inside even if you don't latch the side buckles. (Provided you're not in a stunt plane doing barrel rolls!) The flaps on the side kind of look like they are loose, but they're actually sewn down. Not sure if I'm making that totally clear, here's a pic:
Where the arrow is pointing, those two pieces are sewn together so they're not going to flap or be loose. Obviously if you're in a crowded subway or somewhere that gives you that creepy "I'm about to get pick-pocketed" feeling, you'd want to batten down the hatches for extra security. I hope this info helps, please let me know if you have more questions.
Okal - I do believe you aim to misbehave!