It is not unusual for a police officer to stop a car for a traffic violation and then, after finding evidence of another crime, charge the defendant with additional crimes but never write the original traffic tickets. Sometimes this can help in a motion to suppress. It is obviously a very good thing that he passed the field sobriety tests. I assume that he has not been charged with DUI. The possession of marijuana may well be subject to a motion to suppress. If the court agrees that the search of the pocket was without a warrant or a valid warrant exception he should order the evidence suppressed. This means that the prosecutor would either have to dismiss or appeal the case. 4th Amendment law, search and seizure, is a complicated area and needs the attention of a lawyer experienced in criminal practice and drug cases as well.
Simple possession of marijuana, assuming no priors, is a class A misdemeanor. The possible sentence for conviction of a class A misdemeanor is one year in the county jail and a fine of up to $2,500. He needs to speak with an attorney immediately.
Legal disclaimer: Legal disclaimer: Patrick M. Lewis, (913) 558-3961, firstname.lastname@example.org. This answer is intended to provide general information about the justice system. It does not provide legal advice nor does it create an attorney-client relationship. It does not provide the basis for making decisions about a course of action. Legal advice requires more communication and information than is possible in this format. Many important considerations and factors need to be investigated and discussed before an attorney could give legal advice about this issue. Before making any decisions about a course of action readers are strongly encouraged to contact a lawyer and secure an attorney-client relationship. Readers must also understand that this format does not provide for confidential communication.