Over the course of our lives we will go through thousands of pairs of socks. Most of the time the bottom of the sock is what is worn out. The top portion is usually in good shape, particularly athletic socks.
When the heel is worn through or the sole thinned out, simply cut along the portion that separates the foot section from the leg section. You now have the worn bottom for a one time cleaning of something around the house, be it cleaning up something oily or chemical laden. If it is just general cleaning, of course they can be reused by washing them with the blue jean load.
Now the top part I have found is perfect as a water bottle cosey. Very stretchy and fits over many sizes. Not so much the metal bottles that are around, more like the empty Sobe bottles or similar size. No more sweaty bottles and wet hands.
Another use I have found for the tops is they keep your wrists very warm in winter. You just put them on your wrists and they go about about half way. Keeps the drafts out, helpful even with long sleeves. Also gives the wrist some support, like a light splint.
I also have a mountain bike and the handlebars are rather painful to hold onto. The rubber bites into my hands. I put a sock top over each handlebar and wear my riding gloves and it helps very, very much.
Now I haven't tried this idea, but I think it would work, as I am a sewer. If a cuff of a play jacket or sweatshirt is frayed or oiled up, you could replace it with part of a sock top. Good elastic and comfort. The best socks I have found are the type the postal employees wear. They are navy blue with black stripes on top. Of course they go through these socks within a year and a steady supply of worn are at hand.
So go through that sock bag and give them a new life. Here's to reusing!