To prevent grated cheese form sticking together, just add a little flour to it. It does not affect the flavor or appearance. Then put it in the freezer in a Ziploc bag. It's easy to get what you need, without wasting cheese that is clumped together. I make lots of cheese toast, so I want to be able to sprinkle it on evenly.
Editor's Note: Restaurants will also add a little cornstarch to cheese as they grate it to keep it from sticking together.