That's a great question and the answer is in understanding what you want to do with the power first.
If a tree fell in your neighborhood and took out the grid for a week in the middle of winter: what would you consider the right balance of necessity and luxury?
When you're in the dark a light is everything. In this day and age internet and phone access is crucial; information is like another utility. How about a movie and charging your laptop while you're at it?
To us, when you have nothing else, that is enough to maintain the comforts and essentials needed to feel at ease in even the harshest scenarios.
Enough power to keep going is all the power you need when you have no one to rely on but yourself. But, "enough power" as a rule is when the amount you have matches your needs and the needs of your objectives.