There are many legitimate kinds of bug out bag. The carry kit is a pack of some sort that you would want nearby under all ordinary circumstances. A sort of extended pants' pockets. The bailout bag is a kit to travel with that would take care of food, drink, work, and recreation for an extended trip. Think armed forces personnel in transit or hiker heading into the woods. But what you are looking for is a personal, portable Red Cross and emergency services station.
I played around with a few carry kits. Noiw I'm down to one small and one large. The small is a S.O.B. Pack Rat and the large is a County Comm Bailout Bag. depending on how light I want to travel or how much else I want to add for the day.
But when it comes to TEOTWAWKI -- The End Of The World As We Know It -- you need a completely different philosophy. For a start, structure one good backpack around this sort of equipment mix:
QuietStorm's pack.
More to the point, you will need extended access to food & water, medicine & first aid supplies, weapons & tools, and shelter & transportation. So this is a good time and a good exercise for you to begin defining and assembling a lot more than just a quickie emergency kit.
There is an incredible amount of reading available on this. I agree with the others. Search this forum for bugout bag and you'll probably be researching the answers for hours.