E.M.
My parents have a pool in the back yard and we always managed to magically get 6 to 12 beach towels in late August. We would ask around to return them at 1st but never did find an owner to any of them.
I would teach your child to put her socks INSIDE her shoes. It is what I have done and we never lose socks now (though sometimes the kids will insist on wearing the socks 2 day in a row...)