Answer:
I fly when I'm on and float coming off.
Poor people have it. Rich people need it. If you eat it you die. What is it?
What do people spend a lot of money on every year, but never want to use?
I am flora, not fauna. I am foliage, not trees. I am shrubbery, not grass. What am I?
By myself, I'm practically nothing. Worthless as a leader, but when I follow a group, their strength increases tenfold. What am I?
Though not a plant, has leaves. Though not a beast, has spine. Though many wouldn't need this thing, It's more valuable than wine.