I've kept a collection going over the years of end pieces, blown out mistakes, any texturally interesting bit of film without a proper image on it. I even developed some 70 year old 9x12 sheets found in some ancient film holders just to see what I'd get. They were blank but had oodles of scratches and unusual textures. Not sure what I plan to do with them, but I do find them fascinating. Attached is a scan of one such sheet. It's black and white, but I left the color as the scanner interpreted it. Levels compressed a bit to show texture.
EDIT: Sorry, this reply may have been a bit off topic. I thought you were talking about the blank spaces between images and not printing contiguous frames.