I try to keep my stash very small -- one bin. There are 2 options for leftovers. The first is to assign them to a new quilt asap, in which case I cut them into what I need. The second option is to add to a crazy quilt I've decided to start working on to use up my scraps because they're starting to get out of control. I do occasionally have a few pieces of fabric that I really love & hope to use in the future. I mostly do hand applique work so I love Fat 16ths (9x11") -- and love buying that size at LQS, also. I also like 2.5" strips as they are great for sashing & borders.
Because my stash was really starting to get to be too much -- mostly because I had a 2nd whole bin (sweater size for under the bed) that's in a storage closet -- I decided to open up some of that fabric to my 4 year old niece. I made her a flannel board & let her pick from certain fabrics -- especially JAF/HL fabrics from when I didn't know any better. I bought a pinking blade for my rotary cutter & kept an old mat that got warped which I use for pinking cutting. She picks 1-2 fabrics that she really likes most each time she comes to visit & I cut them into doll clothes for her "design wall". I'm thinking this next time I might also cut her some 2" squares so she can do some quilt layouts as well. She absolutely loves that thing; it gets those fabrics out of my stash; and I get the joy of seeing them up on a design wall whenever I go to visit her, too.