I buy Pattern Ease...it's inexpensive (especially with a coupon

) andyou can find it at almost any fabric store with the interfacing. It's easy to trace and holds up well. I make sure to put all the pattern info on the traced pattern, including pattern company and #, as well as all markings. I just keep the whole shebang (store-bought pattern and my traced pattern) in a large zip-lock bag. Works like a charm!