You should bring evidence that proves the argument you are trying to make. For example, if you bought a car from a reputable dealer without knowing that it was used in a drug transaction, bring the documents showing that you bought the car from the dealership. You should also bring any evidence suggesting your belief in the legitimacy of the purchase and your lack of knowledge of the car’s history. For example, you could get a letter from the dealership saying that they also did not know the car had been used in a drug transaction.
In our example, Steve’s best evidence might be a time-stamped receipt from the check casher or a written statement (also known as an affidavit) from a clerk at the check casher stating that the clerk had given Steve the $900 in exchange for the check from Steve's employer on the day of the traffic stop.