In survival, few things are talked about (and for good reason) as the bug out bag.
However, too often this is looked at too much from a survival perspective. The truth is that if you want a really GREAT bug out bag, instead start thinking from a "backpacking in the deep wilderness" perspective.
In deep wilderness backpacking, you have to carry literally everything that you need for the entire 10 day trek. Shelter, food, a way of food preparation, water, a method of making water safe, something to sleep on, and so.
And much like the idea of a bug out bag, everyone "carries their own weight" except the very young or old.
Not only that, but deep wilderness backpackers actually make "bugging out" an incredible amount of fun.
So where am I going with all of this?
If you truly want to understand how to create a bug out bag and how to THRIVE during a situation that requires a bug out, then consider learning deep wilderness backpacking.
In this regard let me highly recommend checking out:
The Backpacker's Field Manual, Revised and Updated: A Comprehensive Guide to Mastering Backcountry Skills
This is a great book that can explain all the ins and outs to living "in the back country". The same set of skills that would serve you well in a bug out.