I've been crocheting since I was 5 years old. Back then it was just little chains that I used as belts or hair ribbons, but my skills progressed with time. Over the years I have made umpteen blankets, hats, scarves, the occasional dress, and even "tropical sore bandages" (as part of a church service project). In recent years, I have become disaffected with the craft. Does the world really need another frilly synthetic-fiber crocheted candy dish? Sure blankets and scarves are useful, but I recently discovered where to buy recycled-content polarfleece (http://www.milldirecttextiles.com/dept2.asp), which makes up into a blanket or scarf faster, warmer, and with no greater expense than if I had bought the yarn needed to crochet one.
Last year I came up with a useful, if unusual, outlet for my old skill. The city in which I live is very proactive about recycling. Virtually all plastics marked for recycling (with a number from 1-7, which indicates the specific type of plastic used) can be placed in the recycling bin (although I have no idea what becomes of the plastic once it is collected). Plastics that are not marked, however, are still frowned upon. And a surprising range of plastic bags, usually food packaging, are not actually marked. Sometimes, if the bag is essentially clean (like those ridiculous double-bagged loaves of bread), I put it in the recycling anyway and hope for the best. If it is filthy or was used for meat, I consider it to be trash. If it is not filthy, but not clean, I hate to waste the water to wash it when there is a good chance it will only go to the landfill. So I crochet it.
To make tarps like this, I cut plastic bags open into long strips, knot the strips together, and stitch the resulting "homespun" yarn into a circle using the largest crochet hook I could buy. I could do other shapes, but round is simple and works for my needs. This one is about 30" inches across, the result of unmarked bags I have been collecting since about October. I usually sit down and work on it whenever I have 10-20 bags to use up. The ones shown at the top of the tarp are 25 lb pinto bean bags- it was time to top up the food storage. By the end of the summer, I should have amassed enough bread, frozen veggie, marshmallow, and various other bags to make it large enough to cover my typical 3-foot compost pile.