When I run out of anything that I need to replace in my sewing room, I write it into my tiny spiral bound notebook that stays in my purse. I can attach tiny pieces of fabric on the page by stapling it to the page too. I helps me to stay organized while shopping. Needles, sewing thread anything that I have run out of.
And when you have most of the fabric but need a couple more, it helps to have the sample right there.