I use a small post-it note. They are 2x2 inches and have sticky on the whole note. I write the amount of fabric and the date. Attach with a small glass head pin. I've never had a problem with any rust from the pins. We have central A/C on in the house so maybe that makes a difference.
One of the LQS has a label with the fabric info, yardage amount, and sku #. I leave that right on the fabric and no issues.
I tie any collections or already purposed fabrics together using a tie made with scrap fabric.