Get a Shemaugh and learn how to wear it in different configurations. It's a habit I picked up in Iraq. Maybe a little out of place here in the states, but I don't wear it for style.

Brigade Quatermasters sells some darned good ones. They also have a how-to for how to don for desert conditions. I find turban style with the back draped down my bare neck to be an effective sun barrier.

Sometimes I wear a Columbia sportswear super ventilated boonie hat instead.

Wiley-X sunglasses are probably some of the best for desert wear you'll find.

You can never carry enough water. I have a three liter Motherlode pack from Camelbak that is effective for a 4 day pack in the desert, provided I add another couple liters of water.

Carmex lip balm really helps with chapped lips. It tastes/smells better than chap-stick or bag balm.