I remember there were times when the cops would find some marijuana or bags of coke on a car and try to figure out who was going to get charged with possession. It's usually the person who was sitting closest to the drugs at the time of the arrest, but that's not always easy to determine. I've seen police officers tell occupants that they would all get busted on drug possession charges unless one of them owned up to it.
Back in the day, some of my friends hoped they would only get a simple possession charges, because the next step up would have been possession with the intent to distribute. That's a much more serious situation, because the amount clearly exceeds "personal consumption".