Today I recycled some grocery bags into plastic strips for knitting. I made a mesh bag for hanging onions in my kitchen...
URLS for prepping the plastic:
http://www.nezumiworld.com/crochet_038.htm
http://www.marloscrochetcorner.com/bag%20cutting%20instructions.html
I used the loop method to make double thick strips and then knit them using the large yellow KK loom. I crocheted the cord for the drawstring with just a chain stitch.
TIPS:
Make your strips about 1 inch wide. Anything less than that tears too easily. when combining strips, go easy on them and go slowly. Don't pull hard at all or they tear.
Wal-mart bags tear REALLY easily so be careful with them. Thicker bags, like those from Target or Office Depot are better, but of course, we don't usually have access to as many of those.
Use an old hook for the looms when doing this as the tension may make your hook bend. It can be bent back into shape but may be weakened by doing so.
LIft the loops over the hook, don't pull them out and up or they will tear and mid-project, this sucks. You'll have to try to tie the torn ends together and you'll end up with holes in the bag. It will still hold, but it looks ugly.
If you want to crochet the strips instead of using the knitting looms, use a Q hook. The looms give more of a mesh look - if you want something closer/a tighter weave, then crochet them instead of using the looms using the single stitch.