Read about, or watch youtube or other videos, on making a survival shelter. It doesn't take much knowledge to break off and gather branches, the leafier the better, pile them up and get underneath or in among them for warmth or shelter from the wind. Enough pine branches can shed water too. Find a fallen tree and lean branches up against it to make a small shelter you can crawl into. Have another pile handy to pull into the doorway after you get in, to further contain your body heat and keep out wind. You won't suffocate. Enough fresh air will filter into your shelter to provide you with oxygen.
If it's winter, dig a hole in the snow, line it with branches and pull more in over you. Even a snow cave with no branches to put in it will be warmer than the outside air, plus provide protection from the wind. If your car gets stuck in the snow and it looks like it'll be a while before you're rescued, or it's so cold you won't survive even a short stay, rip your seat covers and pull out the stuffing. Put it inside your clothes for added 'warmth'. I realize this isn't bug-out bag information but it's still good survival information.
You can make your bug-out bag as complicated as you want. Here's a website that specializes in survival kits and packs, and carries a wide line of things you can put in your bug-out bag:
But this post is about the uncomplicated bug-out bag; the simplest bag you can put together. For a simple, uncomplicated bug-out bag that you can assemble with what you have on hand: a layered combo of jackets, a spare pair of socks, a spare pair of underwear, matches and a lighter, a couple of water bottles, a handful (or more) of hard candy (mints, butterscotch, whatever you like), a big bag of peanut or peanut butter M&Ms or trail mix. That is the basid stuff that will keep you going for a few days.