Rich people need it, poor people have it, if you eat it you'll die, what is it?

nothing

Explanation:

The answer is nothing. 

If you think about it, many poor people are living with very little or nothing every day. On the contrary, rich people buy so much with their wealth that they don't need anything else. If you eat nothing, you will eventually starve to death. 

Hope this helped you out! :3

one context clue that me find the meaning of luxuriance was that the base word of luxuriance is luxury, so i think that luxuriance means something that is luxury, or something luxurious.