I'm still feeling my way when it comes to scraps. I'm not fond of extremely scrappy quilts, as I am not confident in my color choices - it ends up looking muddy. I keep items that are less than a FQ sorted by color.
The sizes I use the most mirror the pre-cuts so I can mix and match easily. If I only have a few squares around 10 inches or more, I like to do the magic eight (two 10 inch squares sewn 1/4 inch from each diagonal and then cut on the diagonal & and into quarters) by pairing it with white/neutral or another solid.
Then I have a neat stack of eight 4.5 unfinished HSTs. When I do this I also try to use the white/neutral with a few matching solids too, so I have several similar stacks to use.
At least it FEELS productive. HA! Now to use the 300+ random HSTs I've accumulated. : )