Whichever side is which, I always seem to open it the wrong way. Which leads to whatever is on the “strap” side falling out all over the place.
Last trip I used the “strap” side for large packing cubes, so I didn’t have loose stuff falling all over. I also added a pouch of things that weighed about 2 lbs, just in case my bag is overweight. I could easily grab that pouch and put it in another bag. My luggage scale never seems to watch the airport’s scale.
In the zippered side, I put smaller packing cubes and other loose things.