Apparently, a lot of you are finding those rubber pole tips -- damn, I need a pair of those, but haven't found any!
On trail, I've mostly found the usual stuff, abandoned hat, gloves, bandanas. My best haul was a yellow Garmin GPS (which I can't find around the house, no matter where I look - Karma!!!). I examined it carefully, and started it up, but there was nothing that listed the owner. If it's garbage, we usually pack it out (my husband brought out an old Mateus bottle today -- heavy SOB).
Living in the desert, we don't touch water caches. It could be a matter of life or death for someone -- wouldn't want to be morally responsible for someone's death.
Off trail, I've found lots of stuff: a powder horn (!), shell casings, pens, bottles and cans (some old), bandanas, the odd climbing nut or carabiner, bits of old climbing rope -- and a (used) pair of boxer shorts printed with roast turkey legs (!!!). I can't even imagine what the story was on that last item. My buddy & I couldn't stop laughing -- he put them in a plastic bag, and brought them home!
As for stuff I've lost, well... I'm probably not ahead of the game over all.
What I have NOT found: The Lost Dutchman Mine.