The most likely interpretation of this sentence is that someone used one sock to store something, so the English translation follows suit. But it's not the only possibility. It could be about multiple socks used as multiple pockets.
Similarly for the socks-in-shoes sentence. I would take it as a pair of socks stuffed into a pair of shoes, so I'd translate it as plural. But it could as well be just one sock in one shoe, or that all the shoes (need to) have socks in them.