This is my favorite case of all time. People don't realize you have a macbook and therefore don't take it. In my opinion I would not buy a case for the charger and case. I would buy a case for the macbook air and then carry the case and the charger in a separate bag.
Here is an example of a case you could put your charger in. You might as well just buy a bag when you get to that point in my opinion.