Bro, for underwear, go for boxers. I'm a hiker, so I prefer the "boxer briefs" which sort of are like bicycling pants. They really help prevent chafing. Here are some mesh ones that I've used with good success on my hot wx hikes in the SW, including many in AZ. Was stationed in AZ three separate times. http://www.rei.com/product/731994 They also have non-mesh ones. The mesh ones breathe better, but the non mesh ones are a bit more durable. I use the mesh for summer and the non mesh for cooler wx.

These are the pants that I use for hiking: http://www.rei.com/product/746908
100% nylon, lightweight, strong, quick-drying, breathable, zip off legs, and pack really small. Recommend them highly. Bought some cotton ones about the same time. Cotton ones lasted a year or two, but the nylon ones are still going strong (albeit tattered). Of course in wx where it's not going to get too cool at night (>70F?), cotton will retain moisture and keep you cooler. I basically just use the nylon year round so I don't have to have muliple types of hiking pants. Keeps it simpler.

The shirts I like are the nylon ones from Sportif. Sometimes REI will carry them, but I get a lot of good deals at SierraTradingPost.com. Again, they're light, pack small, strong, breathable. The collar, when turned up helps keep the sun off my neck when needed. Some models have an extra fold in the collar that when unfolded covers even more of your neck. The velcro pockets are great for sunglasses, a compass, or even a small camera. Sleeves roll down for sun protection as well. Not too much selection on Sierra Trading Post right now but here are 3 of that brand:
Sportif-USA-UV-Wind-Knot-Shirt-Long-Sleeve-for-Men
Sportif-USA-Drake-Shirt-Long-Sleeve-For-Men
Sportif-USA-Kilimanjaro-Nylon-Shirt-Long-Sleeve-For-Men
I find that they're plenty comfortable after a wash or two.

For shooting, if your firing from the prone, the nylon will be a little thin in terms of providing padding from gravel, etc. If you're firing prone from a mat, no problem. If not, the US Army type BDU's (now ACU's) are great. Google them on the web or go to your local surplus store. I'd want plain kahki were I trying to avoid a military look. The real USGI ones are incredibly tough (I'm talking about the temperate weight 50% Nylon/50% Cotton ones here; the hot wx ones are great too, but not quite as durable). I got issued a pair of BDU pants in 1983 that I still have and are (more or less) wearable. In all fairness, this was a pair I didn't use as much as some other ones I was issued, and I don't wear them on a daily basis -- just outdoors stuff on weekends -- but still, 25 year old pants is pretty good. They're now threadbare in places, have some holes, the pockets have ripped out a bit, and the butt seams are starting to fail, but they've stood up to years of hiking, bushwhacking, and volunteer construction work.