I have two buckets - one that is all self made kits and the other has sizeable pieces of fabric that have been left over. I pull from these when doing something small - like a block for my calendar wall hanging.
Just today I purchased all the fabric for a specific quilt - including the book and backing fabric. It's the Camelot line from In the Beginning - I have everything I need to make a Merlin's Magic blue wall hanging; it will go (with the book) into a large ziplock bag and into the kit bucket. That is the first time I have intentionally bought something to put in that bin that I know I won't make until later. But this particular fabric is BEAUTIFUL and I knew I wouldn't be able to get it later so I just did it. I even pulled the $$$ from "Mommy's Mad Money" so no one is any the wiser!!