I am going to be honest with you. Every time I have tried to do this, I end up not getting much into the donate pile. I pull much of my new quilt tops I make from my stash, so I don't feel the need to waste time and money to get rid of it. The one thing I don't use much is the pre-cuts. I have bought books to try and figure out a good setting for them. But, as yet I have not made one. Sigh... I suppose I am too cheap to let that hard earned money I spent on them go out the window.
Now one thing you can try is to put the type and color of fabrics together to make it easier to see when you make a quilt top. I find half of my buying mistakes are repeats I forgot I had.
I have gone through my patterns and shared many with the Assistance League secondhand store. They support many programs in our area. The food bank, kids school lunches and they have a program that sells senior citizen crafts for free. I can see where it all goes to. You gotta love that.