The FIRST method is think of it as taking a 3-day camping trip. If you were to leave your home with nothing but a bag or car, think about essential things you would take with you. Your goal is to make the trip easy, comfortable, and fun.
Thinking of it from this approach, you would start having ideas, and more importantly, you are not afraid or overwhelmed at all. If you want to take it a notch higher, and be more intense about the visualization, you can change the question to "what would I want with me if I suddenly became homeless," or "if I had to sleep out for the night, what would I truly want to have on me?"
The SECOND method is more personalized to you. It will help you to think of what your personal priorities are. The question to ask is, if I was suddenly left out to taking care of my own self, what would I need in the first 2 hours? What would I need after half a day? And what would I need overnight?
My priorities might be different from yours. For me, I am afraid of being hungry. And also for me, I get cold easily. For this reason, a lot of my preparedness is centered on short-term / long-term food storage and all sorts of state-of-the-art gears that keep me warm.