I salvage buttons, zippers, buckles, straps etc from all old clothes (destined for rags) & school bags and re-use them on other projects. I've also been known to cut away the good bits from a stained garment and save them for applique or small sewing projects.
I've also bought clothes from the thrift shop just to get the fabric and the trims!
I am fortunate to be able to get hold of "industrial waste" from local companies near my home to be used for various craft projects,
A huge burlap bag from a local peanut processor became the material for a few mini Santa sacks that I used for decorating! The excess burlap was used to cover a shoebox for storing odds and ends
Newsprint roll ends from the local newspaper - I get what seems like MILES of paper on one roll end which is used for gift wrapping, DD's drawing paper, homemade sewing patterns etc. I have a roll end that I bought about 18 months ago, has been used regularly since then and I'm guessing that it will still be here for another six months or more before I reach the end
Off cuts of card stock, silver paper (some of it is adhesive) from local printers and label makers
Broken tiles from a nearby warehouse for DD's mosaic projects (I also save broken dishes for that purpose)
Shredded paper from offices to be used for gift baskets
My husband nearly died laughing last week when I salvaged bits of mirror I found in the street. There was a rounded mirror on a pole near my home - the kind that is designed to help drivers see traffic at "blind corners" Someone vandalized the mirror - so I gathered up the bits! I get free craft material and the street was a little tidier and safer as a result of my effort