I've found a bunch of tools including four various size Vise-Grips, three screwdrivers, two claw hammers, 4" and 6" Crescent wrenches, several combination wrenches and, like you, a rusty but functional Leatherman tool. I can only assume these have fallen off of commercial trucks as they are by far my most common find.
I once found a wallet just outside a gas station. The owner had put it on the roof when he went inside to pay with a credit card and had driven off with it still there. Yes, I did return it to the rather grateful owner. I also found $2.67 in loose change all in one place but was not able to return it.
I did find a cell phone but it had been driven over several times and was completely trashed.
Every ride is a treasure hunt!