As simple as this question is. It is yet so complicated at the same time (from a philosophical point of view).
Let's break it down with some common answers that some normally answer with.
Some might say, I am the soul that lives within me. Others, might say it is physical, my whole body is me. Those are the common ones. But, it can also be answered as, it is the ideas, the mindset that one has. Or, the experience that one has gone through.
All of these answers are good. It gives a meaning to the person who answers them. However, when we talk, we do not say I am a hand or an idea. It is considered nonsense in a way. We tend to say, my hand, my ideas...etc.
So, the question is in the definition of one self. As far as I have read, it is one of those questions were you just keep it as a question as it is wider than the answers we are answering for it so far.
Disclaimer: This thread is just for entertainment purposes. I intended to make it as a thought-provoking piece only.