I hate to sound like a sheeple, but there is no 'real' planning for this case. We can only be aware of our surroundings at all times and hopefully be able to 'do' something correctly when/if the time comes because we're always running scenarios through our minds every time we go anywhere.
The planning comes from an analysis of these types of situations. what are you likely to face? As Kathy puts it, Are your skills up to task?
Is you equipment up to task? Are you a world class shooter, if you had your tricked out 1911 but find yourself armed with you pocket 380?
Hope is NOT a strategy, you will not rise to the occasion, you will default to your training. Running the scenario though your mind is an important part of training, it is the mental preparedness.
Situations like this are why I train hard, why I practice 50-100 yard shots with the gun I carry, why I carry a fighting gun and not a pocket gun. The situation may not call for a gun, but it may. My first responsibility is my family, I will see them safe first.