I use a tracer's paper, which is like a very lightweight interfacing. Because I make so many clothes for the GK's, I just trace out the size I need, label it all and I have a permanent copy. And with the Ottobre patterns (and now the Jalie) that I use I just fold them up with the original pattern in a clear ziplock bag slightly larger, to hold the extra bulk. And the patterns that I alter are cut out of the same paper, once the altering is complete. I buy it on sale in large quantities, then roll it onto Xmas paper rolls to store it flat.
Asking a quilter to mend something is like asking Picasso to paint your garage