If your car is stolen you must first notify the police immediately, then tell your insurer. However, be prepared to wait a while in case your car is recovered - many cars taken without the owner's consent are soon found abandoned.
Similarly, if property is stolen from your car tell the police immediately and then tell your insurer. Most comprehensive policies protect you against loss of or damage to rugs, clothing and personal belongings that are in your car, but policies will set a limit on the value of such property. Check your own policy for details.