easy: lay bag flat and cut it into 2 (as big as you can make them) circles (enough for 2 little ghosts). 

Stuff equal pieces of the bag cuttings that are left over into center of each circle. Twist into a ball (this is the head) using sewing string tie the neck (and leave a long tail to the string to use for tying the little ghost to dangle from a tree) take a black permanent marker and draw a big circle mouth and two eyes on face of ghost and hang. They blow real good in the breeze and rustle. Looks really neat. 

Lots of fun to do and at no cost so to speak.