I love using 'found' items that are common place but are not considered "hobbyware".
I have used these sheets myself and use them wherever reinforcement is needed. Since I mostly do 1/2A, I use them around engine mounts and landing gear.
A little bit on the outboard wing tip.
I can also use them in place of the cloth hinges as were supplied in kits once upon a time.
Just cut a strip for each side of the elevator and after the plane has its finish, just a little Duco cement and when they are on the underside, you would never know it!
Glad to see others finding this practically free stuff useful.
Robert