You might want to read up on the laws regarding digging through trash. If the trash is on your property - it's illegal. Even if its in your driveway waiting for pickup, it's still illegal to go through. Also, In most states dumpster diving at any business is considered a felony.
As always, depends on state and local ordnances. If you are on private property you can always get hit with trespass, but the actual trash picking is typically legal. Many licensed PIs make their living going through other people's trash. In short, buy a shredder.
You are correct in terms of state and local ordinances, and I did do some more research and came up with the landmark case of CALIFORNIA v. GREENWOOD, 486 U.S. 35 (1988) where this very issue was argued before the Supreme Court: http://caselaw.lp.findlaw.com/cgi-bin/getcase.pl?court=US...
It basically says if your trash is visible, you can't assume privacy of the contents. If it's inside your garage, then it's off limits. Interesting case nonetheless.
