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.
There was a big hole in the heel of these socks too, but I wasn't willing to do another knit flap so these socks got the "weave across the hole" type of patch. Yarn was sewn across the hole and then woven the other direction to cover the hole. --These are my acrylic house slippers. 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.
And here is the trio of non-holey socks (well, except for the hole for my foot!) Ready to be returned to use! Whew!