Does your insurance policy follow you if driving someone elses car?

No, in the state of Mass where i am from, the insurance is covered for your car only. It will not follow you if you choose to drive another vehicle. You may want to check the state your are in if this is different, as they may have a different type of policy you can purchase that will cover you. With my experience, the only insurance you have is your health insurance if you are driving another persons vehicle.