I recommend switching to non cotton underwear. There are merino varieties and synthetic. I wear some coolmax/spandex boxer briefs I got from target in the sportswear section. I like them so much that I wear these 365 days a year. The hat is less important, but I try to avoid any cotton except for a bandanna. You should at least swap it out for a red sox cap :)
I carry a 300 weight fleece balaclava, liner gloves and waterproof vinyl gloves (from the hardware store, for painting and such) regardless of the weather. Also, some produce bags to slip over my feet. For the 3-4 total ounces this is a huge insurance policy against frost bite, hypothermia or general misery. but then I don't know where you're planning to hike.
I also carry several ways to make fire.