Sunglasses - how else are they going to know you're a pilot?
(The set of permanent markers is hardly a giveaway, and what do you need them for anyway? If you have the Jeppesen non-laminated charts, all you need is a pencil and possibly an eraser.)
Like others said - some stuff in case you get stuck somewhere. Mobile phone, credit card, spare underwear, toothbrush, something to read etc.
Depending on where you're going, it might be a good idea to put a hi-viz in your flight bag. And my flight bag also contains a microfibre rag (kept reasonably clean), a bottle of water, a tiny bottle of soap, a leatherman and a camera. Not essential, but handy sometimes.