Do a Google search on the word "Curtilage", basically the law says that whatever you put out at the curb is fair game and doesn't require a search warrant to get it. We used trash runs to develop PC on so many cases and get search warrants based upon our findings.
Case Law:
The US Supreme Court, in California v. Greenwood [486 U.S. 35 (1988)] upheld that a person does not have a reasonable expectation of privacy in garbage that has been left out with the curtilage of a residence or at the curb for collection and would thereby not be a violation of a persons 4th Amendment right if the garbage was picked up from there.
In United States v. Hedrick [922 F.2d 396 (7th Cir. 1991)], the U.S. Court of Appeals also held that the defendant had no reasonable expectation of privacy on garbage left on his driveway (50 feet from the house, 20 feet from and unattached garage, and 18 feet from the sidewalk) for collection, even though it was on the curtilage, because there was no fence or other barrier securing the area, and it was readily accessible to children, scavengers, snoops, or other members of the public.
See also: Unites States v. Shanks [97 F.3d 977 (7th Cir. 1996)]
See also: United States v. Redmon [117 F.3d 1036, 1038 n. 2 (7th Cir. 1997)]
In North Carolina v. Hauser [464 S.E.2d 443 (NC 1995)] the court held that a police officer who requested that a sanitation worker pick up the trash from the back of the defendant's residence and deliver it to the officer did not violate any constitutional rights to privacy as the trash was collected from the curtilage by the regular garbage collector, in the usual manner on the scheduled collection day.
Links:
California v. Greenwood et al
laws.findlaw.com/us/486/35.html United States v. Booker T. Shanks
laws.lp.findlaw.com/getcase/7th/case/961578.html Unites States v. Joseph R. Redmon.
lw.bna.com/lw/19980331/963361.htm 4th Amendment Searches of Garbage
serv1.law.emory.edu/sites/CRIMPRO/garbage2.html