A polariser is a must! But also don't forget that it's going to be very dusty, so protecting your lenses should be of equal importance to what filters you're going to be taking. It goes without saying but try and make sure you have UV filters on each of your lenses, these will stop any dust from getting onto your glass, and cut out UV in the process.
I would also advise a good piece of kit to invest in is a hurricane blower brush, and a decent sensor cleaning kit. Even if you change lenses for a fraction of a second, you might get dust on the sensor, and that will really show up against bright blue skies.
Have a great trip, and get some fantastic piccy's!