I used to do a post on my blog called Thursday's Throw Aways using recyled materials in my cards and crafts. I've repurposed the insides of security envelopes, the vellum from envelopes received with our junk mail, metal sock clips, expired credit cards, bakery twine, magazine/catalog paper, mesh bags, and more. Here
is the link to those items in my gallery.
Unfortunately, the drawback to doing this is being overtaken by the amount of material that is actually able to be reused!