I've read a couple of historical novels (admittedly not the best source, but they were definitely on the better researched, extremely complicated kinds) making mention of Romanised Brits having a hovering pack of slingers working the perimeter of any mass troop movement to gather up some bunnies etc.
Sling is about the perfect technology for opportunistic use, apart from the ammo it is more or less weightless and in fact could have been used as a strap, retainer or part of another device or tool. You might miss (I wouldn't rely on me to sling you up some supper, unless it was sitting very still and gave me a couple of goes to sight in

) but you've lost very little in the way of calories or bulk carrying and using it.
Only have to look at the "toggle rope" issued in vietnam to see just how many uses people can come up with for a metre or two of decent cordage. I suspect many "braided belts" used by ancient cultures have their roots in slings. Or vice versa. A braided belt with a loop is ideal for carrying all kinds of things, even a simple belt pouch or two and a dagger - worse kit to have when living off your wits.
I also wonder given the history of ancient cultures making hair string ...either for day to day use, or strictly ceremonial... this continues until the present in Australasia and was a big thing in southern US "gothic" funeral art... human hair coiled into flowers and ornamental edging for casket photos... has something to do with the tendency of well known ancient slinging cultures to have long braids on men. I know my hair is long enough (at 70cm or so) and my hairstring making ability is well up to the task to knock up something literally more or less out of nothing.