I save some of my older pieces. In the past I used to cut them up to use as patches in emergency situations. I haven't had to do that for a LONG time though.

I used invisible thread and cut a piece of of hair/lace off an older piece and sewed it in. It worked temporarily, until my sew job came loose. But, I would imaging if you knew how to sew, unlike me.. it would turn out to be durable.