My limit is very low. I'll stop to pick up a quarter every time, but a lone penny never. I've picked up tons of gloves and hats and tools. I have a Ballast Point hooded zip-up sweatshirt that I found on the side of a MTB trail which I love, since it is half sun-bleached and has a couple holes and looks really cool and grubby. I have a bright yellow tech T that I found on the side of the road (somebody riding/running shirtless and dropped it?) that I brought home and added to my commuting-wear rotation. I've found a pair of low-top converse all-stars that I brought home for my son, they fit him and he loves them.
I've found a number of water bottles, but I've got enough (too many!) bottles at home I raised my bar for keeping those. I'm basically only interested in Camelbak Podium bottles nowadays.
I've found and returned 2 or 3 cell phones. I found a tablet with a broken screen, it was able to power up but not really able to display anything. And a smashed iPhone that I kept around for the potential of giving the battery to somebody that could use it. Those two might still be somewhere in the junk pile on my garage workbench.