Answer:
Decline his ride and get a ride from someone else
Explanation:
Although today, it is legal to use marijuana for recreational purposes, there are still restrictions that have to be adhered to. For example, it is legal to grow and consume your own marijuana, however you are not allowed to sell it.
Consumption should also be limited if you are going to need to rely on your reflexes and judgement (in this question, the ability to drive is reduced after consumption). Even if none has been consumed from that bag, there is a possibility that there are still effects on the user.
If you drive the car, and you are pulled over, you can face criminal charges, because you are the driver of the car.