Ive been winter camping in Oregon and Colorado for a couple years now. A car helps a hell of a lot. But other than that:
-Have some kind of shelter: Tarp, tent, Bivy, cave, squat, ect.
-Long underwear dude, not flattering, but lifesaving (Also, Carharts are fucking awesome.
-synthetic clothing, no cotton, cotton kills! (This especially goes for your sleeping gear)
-always carry extra food, ramen and peanut butter, fukin' classic
if you have a small camping stove, take it. Has saved my ass a couple times
-Have a way to make money, I learned to play guitar on the road, and i can make money anywhere
-Keep clean, oils and dirt reduce clothing's ability to keep you warm, wash your cloths often
-Dont believe the "Alcohol makes you warmer" bullshit, if you pass out black-out drunk with no bag in 35 degree weather, you are probably going to freeze to death, processing alcohol makes your body colder, like 3 times colder. Although beer does help alot with falling asleep IN your gear.
-using some kind of insulation from the cold/wind (Cardboard, sleeping pad, pine needles, sand, ect.) will make you alot more comfortable
-GET FOOD STAMPS! lol
-Get a dog or girlfriend/boyfriend
That is how I have survived week-long stints of Sub-zero temps while traveling.