Technically, you only need to buy the minimum required auto insurance in your state. However, when you consider that auto insurance is required in every state but New Hampshire, it becomes clear that the legal minimum might be anything but adequate.
While it varies from state to state, generally the only required insurance is going to be liability. This means that if you are in an accident and found to be at fault, your insurance will be able to cover the other person's damages.
That means that literally everything else is going unprotected.
Comprehensive And Beyond
Basic comprehensive and collision coverage are required if you want your auto insurance to protect you, as well as other drivers. That said, comprehensive and collision only cover you up to a certain extent. You cannot expect comprehensive and collision to cover loans you have yet to pay off (which you can cover with gap insurance). It also won't cover the total cost of buying a new vehicle (which you can cover with replacement cost insurance).
Note that no matter your auto insurance, your policy probably will not cover items lost in a break-in beyond those that can be said to be part of the car itself. When it comes to personal belongings lost when someone has broken into your car, those are likely to be covered on your home insurance policy. Legally speaking, those possessions are like an extension of your house. Therefore, they are covered by your homeowners insurance policy. Even possessions that are generally kept in the car will be covered by your home insurance — assuming you have those possessions listed in your inventory with your provider.
The legally required minimum of insurance simply isn't going to provide you with much protection at all. A basic collision and comprehensive policy will help to protect your car against damages, vandalism and so on. However, it won't fully replace the vehicle in the event that it is totaled. If you want peace of mind, you need to buy a level of insurance that matches your risks.