I read about this in Backwoodsman magazine a while ago, and finally got around to trying it.
  In a pinch, the inseams of jeans can make an emergency sling. Just follow the seam up until you get to the crotch. There, you can cut out the pouch, them continue down the other leg seam, and voila!, a sling!
   I made one out of an old pair and tried it. It was only good for about 30 yard, and could only fire off small stones, but it would probably be good enough to hunt small game. Squirrel and rabbit come to mind
    Of course, you ruin the pants, and if thats the only pair you have, well, then, I wouldn't think it would be worth it.

That was my first sling I used it for golf balls.