Choosing Clothes and Weather...

Dad,
As I am looking over my gear, I am considering my clothing options.
I am currently opting for the lighter weight direction, with something like:
2 Moisture Wicking T-Shirts - Short Sleeve (Mountain Gear or Columbia)
1 Moisture Wicking T-Shirt - Long Sleeve
1 Eddie Bauer Windbreaker Jacket (has removable fleece liner that I will not bring)
2 Cotton/Polyester Blend Conversion Short/Pants
1 Black Webbed Belt (military issue)
4 Pair Polyester Performance Underwear
4 Pair Injinji Toe Socks
2 Pair Merino Wool Light Hiker Socks
1 Pair Vasque Breeze Hiking Boots
1 Pair Rockport Sandles
What I am not sure about is the following:
How cold can it possibly be during July? Weather in California is consistently becoming more and more schizophrenic. Are you bringing long underwear just in case? I have seen recommendations for bringing a warm vest to keep the core warm, what are your thoughts? 
Also, in case of rain, are you bringing rain gear or just a lightweight parka?
I was looking at the Frogg Toggs and a basic set of the performace gear can go for as little as $49.95. Their gear claims to be wind proof and water proof which would eliminate my need to bring the Eddie Bauer jacket. But I would need a vest of some form.
As is always the case with me, I am concerned about the monetary side of things. I am going to buy the short and long sleeve shirts because I figure that is most consistent piece of clothing I will be wearing for the month, I already have the pants and the Eddie Bauer Jacket, and I am trying different underwears to see what I can get that will not chafe.
I am completely sold on the Toe Socks and will use those instead of liners and I will bring Tea Tree Oil to fight my athletes' foot.
With our mutually balding heads, what sort of hat were you planning on bringing. That one I used from Eddie Bauer on our Twin Bridges Hike was nice, but it was too hot and I sweated a lot. I need something similar but breathable. I may actually try getting a military issue desert covert.
Looking forward to your thoughts...
Matson