2. Other driver's insurance company name and policy information
3. Statements and contact information from witnesses
4. Take pictures of the accident scene -- most smartphone cameras are suitable. If you can take pictures of the cars as they sit right after the accident it is best. If you had to move due to safety concerns, then take photos of the damage to each vehicle.
5. All of the evidence gathered at the scene to bolster your position on the cause of the accident.
First, inform the other person's insurer that you have been involved in a crash with one of its policyholders. Relay only the facts of the accident, even if you believe the other driver to be at fault, it’s not smart to just say that. Instead, give the insurer the facts to show their driver is at fault and liable for your damages.
Although you may feel that you have not caused the accident, you might want to contact your insurance company anyway. This establishes your good-faith accident-reporting effort and can aid you if the other party's insurer denies responsibility for the accident or it turns out their insurance was not valid at the time of the incident and you need to make a collision claim.