Not entirely a necessity, but if you can, get a rear bike rack. It will be very useful for you and your community. I had a rear rack, and in some ways, I was damned... I was the block ice carrier. Without a place to carry the ice (which is about the dimension of this rack), you would be out of luck... Doesn't fit in a backpack.

Besides, because you're basically in the dessert, the temperature can drop from hot to freezing in a matter of minutes. This is also where I bungee up my coat after sunset.