I bought a khaki shirt from Sears for ten dollars. Light 100% cotton, khaki (British tan) with two pockets and epaulets and I wear it in the field when I go hiking. I typically layer it with a polypro undershirt or maybe alone. They're not warm, but for a day's tramping through the mountains, it's good.
For desert wear, I wear this shirt. I typically pair it with blue cargo trousers which isn't traditional, but they're more practical than standard gabs, because they have the pockets needed to hold the map and K rations.
Also, the local surplus shop has s/s versions for about 25 bucks. Genuine stuff.