It makes it much easier to make the "yarn" if you use a cutting mat , clear grid ruler, and rotary cutter.
Stack the bags and flatten them on the mat.
Remove the top part with the handles, and the bottom edges.
Cut the bags into about 1" strips.
They will be big circles like this.
Insert one circle inside the other ,
Then make a knot
Keep tieing and roll them into a ball . I separated mine into colors to be able to make stripes on my bags.
Later I will post a picture and tutorial for crocheting the bag.