This sock got two repairs: a knit-like stitch up near the toes and a replacement flap knit to cover a gaping hole at the heel. I didn't have any more of the original yarn, so I used a chain-ply (3-ply) sample in bright yellow and orange. The flap was knit on 6 stitches that I picked up from the heel, increased to cover the hole and then sewn to the sock. We'll see how well this works.
The knit-like stitch is basically a duplicate stitch where I used a needle and the yarn to re-create the knit stitches. The 3-ply patch yarn is bigger than the original yarn and it looks a bit odd.
I don't really care about them as long as they keep my feet warm. If they were handspun, I might have knit another flap.