Well, at least you can put yourself up there with T.E. Lawrence, Dylan Thomas and Ernest Hemingway!
http://www.theguardian.com/books/2009/jan/23/1000-novels-lost-manuscripts
I once inadvertently left a rolled-up set of early 25" and 6" Ordnance Survey maps of the Llangattock area in the high-level net rest between the seats on a train headed for Southend-on-Sea, having got off in a hurry at or around Billericay in late 1984. I tried to get them back through the local station where I got off and the destination station, plus the BR lost property department - with the latter informing me that they didn't have them and, if they received them and they weren't collected within a relatively short period of time, then they would sell them off at auction! The latter was most perverse because the BR lost property department weren't prepared to inform me if they did receive the maps! The worst part was I had spent ages hand colouring the 25" maps to match the pastel shadings on the original copies, from which the new copies had been made in the British Library Map Library!
And, similarly to you, back in the 1980s I photographed a set of 35mm slides in the then new extension to Llanelly Quarry Pot, with one showing the
Michelin Man formation in the streamway, another of Mike Green at the
Mike's Beard formation and a set up in the Totem Aven Series. Many of which I'd dearly love to be able to include in my forthcoming book on 'The Caves of Llangattock Mountain'. However, whilst living at Peter Bolt's house in Cardiff, c.1988, I lent the box of slides to some caver who called in and was exploring Llanelly Quarry Pot at the time, and about to give a lecture on the finds to some rotary club (or other), and he NEVER RETURNED THEM ! ! !