Kyle Glenn, 22, was pulled over for a traffic violation on U.S. Highway 101 at Gravenstein Highway around 12:40 a.m., police said.
During the stop, officers discovered marijuana, about half an ounce of cocaine, and some heroin and packaging materials, according to police.
Glenn was then arrested, police said.
His passenger, Stephen Sisco, 19, was also arrested after officers found him to be in possession of brass knuckles and cocaine, police said.
The two were booked into Sonoma County Jail on charges including possession of narcotics, possession of narcotics for sale and possession of an illegal weapon.