I am a veteran dumpster diver and trash pile junkie.
I've found everything you can think of, INCLUDING a Stevens model 67 12 gauge pump shotgun. (Sorry, no AR's or pistols yet...but there's hope!)
In my area, legally speaking, trash placed for collection is the property of the waste management company that picks it up, but they do not assert any exclusive rights or forbid people from browsing and taking what they want. I know of no case where police have ever bugged anyone over scavenging in trash piles. In fact, they just don't care as long as you don't make a mess.
If you have sensitive info that is to be thrown out, buy yourself a paper shredder or toast it on the barbecue grille.
Just a few days ago I found a working Compaq computer that I thought MIGHT be fast enough for me to do something with. So I grabbed it out of the trash pile, took it home, set it up, and fired it up.
The previous owner left a LOT of data on it that I would not want to leave on, myself. Like his resume, family letters, etc. If I bothered to memorize it, I would know a lot about him and his family.
I'll erase that sensitive data and drop this 486 computer off with a thrift shop.
CJ