You don’t need to be a world class athlete to survive a life and death situation. However a good combination of stamina and strength can be very beneficial in those situations. First I always suggest avoiding a conflict when possible. You will need mobility to do that and endurance. Start walking jumping rope riding a bike. The other side of that equation is straight. Start a basic resistance training routine. You might have to fight someone before you can break contact with them. The fitter you are the greater your survival rate. Train two times a week and you will see results.