I pick out several easy scrap quilts that I want to do. One is more specific, and two others are not as specific in sizes ---- I keep three shoe box size rubber maid containers. As I clean up my scraps, I throw them in a box that the fit into or into my big box of scraps. I also keep a 1 1/2 inch container (very small) for the 1 1/2 inch squares for my someday project.
Each person figures out what will work for them. I have been quilting for years and this system has been developed over the years for me and really works for me.