Their has been some good advice given, but no one has mentioned STAY AWAY FROM COTTON!!!! Cotton holds moisture against the skin (whether it be sweat, rain, water splashed while crossing a stream etc...) and will stay wet. The heat from your body then is stolen by the water and you will be miserable all day. Use a polyester (like UnderArmor or any other brand) or silk base layer for the top and bottom, layer on more clothes of polyester, wool, or fleece, and then have an outer layer that stops the wind. Jeans are cotton and are evil when they get wet - agian go w/ polyster, wool, or fleece. I have a pair of pants that are lined with fleece that are great.
Of course, a hood or hat that covers the ears is a must, as are gloves.
As for the feet, a good pair (or two) of merino wools socks inside a pair of proper fitting knee high insulated rubber boots (too tight is bad). Stay away from steel toe boots, as a lot of heat is lost from your feet to heat the metal in the boot.
If you dress right, you won't care when it gets "cold". LOL
