With this one I combined both and made a very useful cord/rope out of mere shopping bags that were going into the recycling bin anyway. The end product is pretty handy. It's very strong, it's waterproof, and it's practically free.
I'd be willing to bet that if I took 7 of these ropes (that I made here) and wove them into a larger rope, I could easily use it to tow a car! No seriously.
Now a few people have made ropes from plastic bags here on instructables, but they twisted them. This project makes a much more aesthetically pleasing braided 7 part rope.
You could use it for pet leashes, fishing stringers, shoelaces, camping gear, jumping ropes, or even a rock sling. The limits are practically endless. It would make a great boy-scout/girl-scout or school project too. For ideas with what you can do with the rope just search here at Instructables for "knot" or "decorative knot". My personal favorite is "Monkey Fist"... look it up!
So make your own and please let everyone know what you used yours for! If you send me a picture I'll post it on this instructable!