Oh, this is a competition which I can definitely win!
In Yr7 DS managed to lose 1 blazer with phone and fountain pens in pocket (eventually recovered by us on vital info from another mother - school no help at all), 1 pair rugby boots, 1 1/2 pairs trainers, 1 towel, 1 scientific calculator, umpteen socks and bits of mathematical sets.
Plus 1 pair swimming goggles, 1 pair school shoes, pencil case, clarinet
and homework diary - all of which were returned to him (in some cases, many times).
I'm sure there was other stuff too, but after a while I tried to block it out to save my blood pressure.
I did make him pay for replacements to try to teach him, and touch wood, it has got quite a lot better. And, to be fair, when the only storage they have is a shared locker, it isn't really a surprise.
I too definitely blame DH who has the greatest of difficulty holding on to his belongings. Before we were married, he once managed to lose the keys to my front door while
he was painting it