As the line in the movie "Forest Gump" says... "There is one item of gear that can be the difference between life and death. Socks. Cushioned sole, O. D. Green. Try and keep your feet dry. When we're out humpin', change your socks whenever we stop. The Mekong will eat a grunt's feet right off his legs."
Of course, you don't need to worry about the Mekong, but you will need to make sure your feet stay warm and dry.
Get good cotton socks, wool socks, insulated, rubber-soled, and any other kind you can get. Remember to get some for other people in your family, and if you have kids, you'll need to get lots in every size.
Check your supplies: how many pairs of socks do you have right now?