What to do if I was in my friend's car and we were pulled over and are being charged for possession of marijuana and paraphernalia?

The first thing you should do is retain an attorney to represent you.  The attorney needs to investigate the facts, determine where the drugs and paraphernalia were located, (e.g., within hands reach of both occupants), whether the contraband was in plain view, whether any statements were made which suggest that you knew the contraband was in the vehicle, and whether the driver made any statements as to ownership of the contraband.  If all occupants allege a lack of knowledge or ownership of the contraband, all occupants will typically be charged with the offense.