I can't remember not knowing how to sew (or embroider or knit). As I graduated from doll clothes to making clothes for myself, my mother taught me to always get a half yard to full yard more fabric than the pattern called for (if I used a pattern--she taught me how to draft patterns, too). Just in case I made a mistake. Of course, fabric was way less than a dollar a yard back then!
I never intended to build a stash and I never bought a fabric without a purpose in mind but when the project was done, there was usually just too much scrap left for me to feel comfortable throwing away. So now I have a stash and some of the fabrics are over 40 years old.
It has been stored various ways over the years, from a cardboard box, wrapped in a plastic garbage bag inside the cardboard box, in a wooden slatted crate and in plastic bins.
I've been going through all these old scraps with my husband, who wrote a database to catalog them. None of them are damaged, all of them look as new as the day I rolled each set up neatly and tied it with a scrap of the same fabric.
The only precaution I ever took with my scraps was to keep it in the main part of whatever house I was living in, away from basements (too humid in the summer) or attics (too hot and too humid).