2.5 inches seems to be my most popular scrap size...I get lots of scraps from friends and oftentimes bits of leftover binding will come my way. Like Bobbinalong, I leave my scraps in strips. I have a rectangular block pattern that takes 20 inches of one color and 12 or 15 of a contrasting color...sorry can't remember exactly right now. I have been keeping the strips I need for this quilt in a plastic box and soon will have enough for the full size quilt. I have started to divide the colors into brights and country colors (think KT, Jo Morton, CW). Then my scrappy quilts are little more "controlled" What doesn't fit into these 2 categories get another box and become leaders and enders for Bonnie Hunter type quilts.
For your 9P's a 10 and a 12.5 inch strip would give you a balanced 9P.
SBG...thanks for the Ikea box tip...guess I will have to go online to check it out.
So much can be done with 9P blocks!