The United States Constitution provides the foundation for the rights that protect all U.S. citizens from intrusive law enforcement practices. These rights should be exercised by everyone in all circumstances, regardless of whether or not an individual is guilty of a crime. Rights are like muscles -- if they are not exercised, they wither away.
RULES OF THUMB
Never leave anything in plain view: Although law enforcement officers must obtain a warrant before they can conduct a privacy-invading search, any illicit material that can be plainly seen by any person from a non-intrusive vantage point is subject to confiscation. An arrest and a valid warrant to search the rest of the area is likely to ensue. A "roach" in the ashtray, a pipe or baggie on the dashboard or coffee table, or a joint being smoked in public are common mistakes that can lead to prosecution.
Never put anything incriminating into the trash: Various courts have ruled that law enforcement officers are allowed to rummage through curbside trash bags without a warrant. A few seeds or stems can then be used as a basis for obtaining a warrant to search the individual's home.
In fact, anything discarded into the public domain can be picked up by the police and used as evidence. For example, if an individual throws an illicit substance out of his or her car window and a police officer sees it and picks it up, the person is almost certain to be arrested.