A perfect example: fused plastic.
Yes, you can take those grocery sacks and cut them into strips and knit or crochet them into bags, but you can also melt them into your own "fabric" and sew them into shapes.
My favorite video tutorial is from Make Magazine, and the pattern for the messenger bag is amazing
Etsy Labs has a tutorial you can read, or they offer a video also.
Katie Crafts has a tutorial for a fused plastic messenger bag made from produce sacks
Dollarstore Crafts made a fused plastic backpack
My absolute favorite twist on fused plastic, is the quilted bag by Craftastica
Fun bag by Betz White
Really creative ideas for plastic fusion (using scraps, weaving strips, adding text,layering)
Timbuk2 bag--how to make an embellished panel video