I own a ton of nylon bag/organizers that have dual zippers and I will open them up and forget to zip them closed when I am done rummaging around inside them. I'll pick them up and waste time having to pick up the contents because there is no way to make sure they are closed.
I was making some paracord cat collars and saw another use for the side release breakaway buckles! A SRBB will come apart easily - perfect for the use that I envisioned? You can get SRBBs in different colors.
This idea works best for bags with dual zippers with knotted string pulls. You can modify a zipper by cutting off a sewn pull and replacing it with a piece of paracord, but that is something that you may want to think about before you modify you backpack/duffel/bag.
This ISN'T an anti-theft fix, it's merely a way to visually be sure that your bag is closed - it does take a little bit of effort to pull a SRBB apart - so, it might help you notice if someone is trying to open up a bag/duffel while you are carrying it around?
Step 1: Get Your Buckles!
I buy all my buckles from an online paracord seller and depending on the color of the bag I am going to use them on? I try to get a color that contrasts - this helps with the quick visual check you can do - if you decide to try this tip?
Step 2: Un-tie and Add the Buckle End!
This step doesn't require too much in the way of illustration or instruction. Un-tie the piece of cord that you use for a pull and add a buckle half. Repeat for the other zipper half.
There are different ways to re-tie the cord - the closer you can get the buckle half to the actual zipper will get you a smaller gap between both zippers.
You could also do this with a steel pull - just thread a piece of paracord thru the eye at the pull or, if you are so inclined and your bag has a solid steel pull?
You can carefully snap the pull off the zipper body and thread the paracord thru the eyelet on the zipper.
Step 3: Done!
Now you are finished!
You can do a fast visual check on your zippers and not have to stop to make sure that every compartment/zipper is closed, I know that this probably doesn't qualify for a real Instructable or survival tip, but I hope that someone can use it!