I have a file that accompanies every one of my stories. It's called "stuff to use later.doc". This file contains sentences, paragraphs, snippets, possibly even entire chapters. Some of it is stuff that comes to mind before I've even started work on an outline. It might be a scene of dialog between two characters, or some information on setting. Then, once I've started writing or editing, I might toss into this file tidbits that are good, and that I like, but maybe don't quite fit into the story as it is right now.
The point of this file is simple: it gives me a place to throw things without throwing them away. I'm not a packrat, but when it comes to writing I don't delete anything unless I know with absolute certainty that it's crap. Even then I may hold onto it for a while longer, just in case.
Point in case: as I continue through a second edit of my current fantasy novel, I just came across a place where it hit me that a short scene I had previously chopped might fit quite nicely. I'm digging into my "stuff to use later" file now and will soon have it back in place.