In the process of making the 'Beads' art installaiton we were making lots of balls made of used plastic bags that we strung together into necklaces. The technique is very simple, stuffing used plastic bags into one another, creating a shape of a ball. those balls/ beads very quickly became footballs and flying balls. craft and play
I found this tutorial on vimeo that demonstrates how to make plastic bags footballs, apparently very common in Africa (there are 2 tutorials, I recommend the second one starting on 03:30).
Remember this tutorial next time you are in need of a ball.