It's a great question. What is enough? There are some other great questions too - Why do so many people always want more? - Does it matter? - What can we do about it? - What can I do about it?
Take a look at this excellent and challenging video. Then visit Conspiracy of Freedom, the people behind it. There are more great ideas, suggestions on how to take this forward (perhaps with a group of friends), and more videos on related topics.
(Thanks to Peter Farmer for drawing my attention to this material.)