I store the pattern or directions with the fabric gathered and then, when it is time, it is all there to begin the project. I do keep a notebook, but it is mostly for stitch settings and quilting ideas. I keep all of the "kits" together so I don't accidentally get into any of the fabrics. That helps me to stay on track.
I too have ordered fabric for a reason and forgotten why. Don't be too hard on yourself over it. Maybe you will remember and all will be right again. Once I ordered three different backings for the same quilt. Thank goodness it was a smaller one and that the extra fabric was nice enough for some other purpose.