Something to remember, most people aren't even capable of carrying very much weight.
I'm a big dude, 6' tall 225lbs with a 52" chest and a 34" waist, and I started my preps with a big, heavy pack. After actually hiking around with my pack on, I learned that I'm not conditioned to carry more than 30 lbs or so. My pack now weighs 20 lbs, without water. It's just enough to get me through a few nights sleeping in a car, in a hotel, or in the woods, and it keeps me mobile enough to jump over rocks or haul ass around the next corner if trouble finds me.
Another point, "survival" does not mean "being comfortable". You don't
need your fluffy sleeping pad, big poofy sleeping bag, tent, freezedried steak dinner, etc. to survive. You can make it through the night (a few nights even) with a warm coat, waterproof poncho, canteen of water, and a small fire.
Building a BoB is a long process, that has to include more time spent testing gear than ordering it on the internet:
Step 1: Order crap that other people say you need, and order too much of it.
Step 2: Pack it into a bag that is way too big, that you aren't capable of carrying because it is too heavy because you packed too much crap that you don't need, and don't know how to use.
Step 3: Use it, overnight hiking or whatever, and realize what you used, what you didn't, and what you had no idea what to do with
Step 4: Redo pack completely, knowing what you are doing now
You'll probably end up with more water, less food, less comfort items, etc. than you started with.
When I think of a SHTF situation, I'm thinking of either a pandemic or chaos and anarchy has broken out. I'd probably head towards the mountains in my area.
Good luck in the Mountains, between the people who live there and don't want you there using their resources, and others who plan to "head for the hills" and might need your nice gear.
Do what you have to do, but "heading for the hills" is a bad idea, generally.
Of course if I'm missing something
First aid supplies. If you aren't trained in its use, get the training.
Injuries and the elements are more likely to kill you faster than starvation or dehydration. Your BoB should include what you know that you can use to put yourself back together (temporarily) and stay warm and dry first. Then comes hydration, as much water
as you can carry which again is a personal thing and varies from person to person.