This is a copy-paste of what I just posted on a local forum, in a thread where others are agonizing about heavy packs--it's just an extension of what Ben has told you:
The "Big Three" (sometimes the "Big 4" if the sleeping pad is included) are often the place where many of us can most easily cut weight. Sometimes the weight savings can be spectacular, sometimes more modest. Here's where I was 6 years ago and where I am now (the old weights are approximate, and tent weights include stakes):
Tent: Sierra Designs Clip Flashlight, 5 lbs.
Pack: Kelty external frame, 5 lbs.
Bag: Generic synthetic bag, about 30*, 4 lbs.
Pad: Thermarest LE, 2 lbs.
Total 16 lbs.
Tent: Gossamer Gear/Tarptent Squall Classic, 27 oz.
Pack: Six Moon Designs Comet, 27 oz.
Bag: Western Mountaineering Ultralight (20*), 25 oz.
Pad: POE Ether Thermo insulated air pad, 17 oz.
Total: 6 lbs. 0 oz.
I'm not necessarily recommending the same items (you'll have to do a bunch of research and decide what suits you), but this will give you an idea.
I often recommend Mark Verber's excellent website, http://www.verber.com/mark/outdoors/gear/index.html
for an overview of what is available, from the latest technology to low-budget alternatives, for each category of gear.
For starters, please, please ditch the cotton (like the thermals you mentioned). Cotton has its advantages in the desert in scorching weather (get it wet and have your own built-in evaporative cooler), but when the weather turns cold and wet, cotton absorbs lots of water, is heavy, is very slow to dry and has no insulating qualities when wet. The same qualities that make a wet cotton shirt feel wonderful on a 110*F day in the desert will send you into hypothermia at 55*F.