Oh come now, he said things
you have personally lost, no need to speak for other people!
Me, myself, I think the thing I lost of the most actual value was my old 3DSXL (which was lost in a move, chances are I actually still have it somewhere, but I got a new one anyway). I also lost my old DS Lite back in elementary school, I was confident I'd find it but never ended up doing so. To this day, I honestly have no idea where it could've ended up.
My Samsung Galaxy S5, which I still have $250 left to pay off on, no longer works. Not sure if that counts as lost though, since I still have it, but I can not use it.