I wear a golden crown and hold the highest rank, yet one trapped step means my entire kingdom falls. What am I?

I'm a word you can use when you can't remember the name of the thing you are thinking about. Oh, and I'm also a candy bar. What am I?

I don’t say cheese, but I make you say it, I catch your big smile in a tiny minute. Click, flash, and later you see what I caught What am I that keeps your face in a spot?

I can bind two strangers, seal a promise, or carry a debt. I can be traded, yet never held. But pair me with a number, a glass, and a drink best shaken, not stirred and I become a signature. What am I?

You can find me in the sand Or in a storm up in the sky. You can find me catching killers Or under a chess player's hand.