I used to use a note pinned to the larger pieces, but than I lost the info when I washed the piece. If you write in the selvage with a pen, it ususally does not wash off.
On my smaller stash pieces, I staple small sticky notes to the exposed corner. Then I store my stash pieces according to fat qtrs.; 1/2yds; 1yd; & more than 1 yard.
I applique, so I have carboard trays with smaller pieces sorted by color & laid out with about 1/2" of each piece visable. Otherwise, I would never remember what I have.