I alwasy like to start at the ground up when it comes to Elk hunting clothing.
Boots- I would look for a good thinsulate boot. 400 gram is usually sufficent for most Elk hunting applications but if its really cold and/or you will be sitting alot I would edge towards the 600-1000 gram style boot. Cabelas has a boot called the "Elk Hunter" made by Danner. They are waterproof, reasonablly light, and have good traction. I had a pair for years and I loved them, plus they got good reviews on the customer reviews. Not to mention the name alone means they have to be good for elk hunting right?Ha!
Socks- I like to use a good wool sock with a liner underneath. Two pairs of socks will last a week so long as you swap out liners daily. The liner will help pull that moisture away from your feet. Thats generally where my feet got wet, was from my own sweat, so keeping them dry is imperative.
Base layer- For a long time I just used cotton long underwear but have since graduated to Sitka
base layers. The cotton kept me warm just fine but after a couple days of use got a bit ripe. So that meant bringing multiple pairs and that just meant more weight and more space taken up. The Sitka base layer has some anti-microbial stuff that keeps it stink free so you can use one layer all week.
Outerwear- Wool! You cannot go wrong with wool. Its warm as anything, quiet and will keep you warm even when wet. It can be a bit pricey but its worth it. I bought some of the Columbia Rag Wool bibs and jacket from cabelas and it served me well. Plus it is much more moderately priced because it is recycled wool. The only problem is that it can be a bit bulky so you wont be running any marathons, but I have never got cold in the stuff. I am giving Sitka outerwear a try this year. Heard nothing but good things and I am want something that will be a bit lighter. Rest assured the wool is coming with me just in case becasue I know it will work.
I hope this helps get you started if you have any other questions or want me to expand on somthing let me know. Have fun this fall! In my opinion Elk hunting is the pinacle of big game hunting in North America, you will have a great time!