I'm a thing that is actually nothing. What am I?

It's sold separately or in a bundle, This bar rules the chocolate jungle.

I’m a box with a key personality, I keep your valuables under tight security. I don’t like to open up You could say I’m a little locked up. What am I?

I grow on trees beneath the sun, and end up in your martini when the day is done.

Happy birthday to you, sings everyone in the room. Someone hands you a knife, now you know what to do.