I have spent the night in a brush pile during a snow storm. If you dress in layers when you go out with the idea that you are dressign for the worst weather that could happen you will always be "relatively" warm.
A minume is to keep some kind of energy food ON YOUR BODY!!! and TWO SOURCES OF FIRE PRODUCTION!!!!
Lighters, even zippos are not 100 percent reliable. Do research and find a second way that you can light a fire with every time.
Hunters and hikers die all the time because they "think" they can do something because they read about it. You have knowledge but you do not have the Skill. Get the skill in your back yard while your able to sleep in your bed at night.
Get a mind set to make fire and you will be surprised all the things you will see that will make a fire.
Get a mind set of "MINIMUM" sleeping requirements and you will not make bad choices building substandard shelter or not put enough on the ground when you are sleeping.
NEVER SLEEP directily on the ground. Even in good weather alwasy insulate the best you can.
I spent four days out in the woods with a pocket knife and a book of paper matches on a bet. For two days I was absolutly fucking misserable. By the forth day I found my groove and a reliable food source. The Secret of neolithic or primitive camping is to spend all waking moments dealing with you situation. If you are sitting be making binding fiber. If you are walking look for shit to eat. If you are getting ready for sleep start two or three hours before sunset and if you can stay in one place and just continually improve your camp.
Anything you can eat....eat. Any thing that is dry is home material.