I've heard of people who save all thread scraps in a clear container, like a bottle. When full, seal it up and you have a decorative bottle.

Oh, yeah, I’m a big ol’ ender / leader quilter! I’m usually doing some string something-or-other as my ender/leader project, or some other specific project with a lot of fussy blocks that need to be stitched together, but lately I’ve been on a kick of stitching together the “waste triangles” from various stitch and flip blocks from throughout the years, creating, over time, a bunch of hourglass blocks in the colorways of whatever quilt the stitch and flips came from. What I’ll do with all the hourglass blocks… Um, I don’t have an answer for that yet! LOL

I'm another one that uses lender-ender system. I heard of the idea from Bonnie Hunter, who I love following. In fact, I'm working on one of her leader-ender projects right now as I finish up my Indigo Way top.

I do that too. I have many blocks now to sew together.

To respond to those who posted regarding my comment on the thread in the waste basket. Yes! There are yards and yards of thread there from taking out a seam, yet we "save" thread with leaders and enders. Saving where we can anyhow. I suppose this is somewhat akin to putting those orphan blocks into something usable. Waste not, want not!
Perhaps those quilts using orphan blocks are somewhat "memory quilts" as each one brings back the memory of "when i made that quilt" and "it was for a special person/a special occasion".