As per the law, having a third party policy is mandatory. Having a comprehensive car insurance cover also helps as it protects you against damages caused to third party as well as your own car. However, while the damages caused to your car are covered, the belongings that you lose from the car are not covered. Comprehensive car insurance covers your car but not the belongings that you keep in it.
There may be times when you would be in a hurry and unfortunately your phone, laptop or any other valuables would get stolen. At such times, you would have no option but to express regret and buy the same valuable using your hard earned money. However, personal belongings add on cover can be of great help as it protects the valuables inside your car.