Just got this for my FSBE loadout: a weapon retention lanyard, called Pistol Leash.
I only have some rather small and blurry pics of this in use. But I think it's this one.
Here are some reference pictures that I found.
And finally here's my more or less completed first line for my FSBE kit.
I could always use the old dump pouch that the Marines used, but I can't seem to find them anywhere. Ordnance1980 made some replicas, but they don't sell them anymore.