I want to introduce a tiered approach that I take that may simplify things. This may help you in development of your kit(s). First you will need to know what event's your planning for. This will determine much of what you pack and how many of the tier's I'm going to describe.
Tier 0-Knowledge: Your most important tier. This may involve paying for training which is why I include it in the tiered system. You may find yourself in a situation where all of your gear has been lost or taken and you have to improvise and your life depends on your resourcefulness. Knowing how to start fires, build shelter, procure food, and make weapons should be part of your skill sets.
Tier 1-EDC/SERE Kit: This includes your pocket knife, multi-tool, wallet, key ring, flashlight, cell phone, and so on. Your cutting tool (pocket knife) being the most important since its the hardest to replicate in the wild and it can accomplish many survival task. It doesn't matter if its a swiss army knife or a $300 tactical folder. It will most likely be your only knife with you when things go sour- since its difficult to get away with a fixed blade in your day to day life. Your Pocket Survival Kit or SERE kit as I like to call it. Typically if you have this and only this; you have had to leave your main pack behind. More than likely your surviving, evading, resisting, and escaping (SERE). These items will be small tools that will aid you and your knowledge (tier 0) should do the rest.
Tier 2-72 Hour Kit/EDC Bag/Get Home Bag: This kit encompasses those items that you have in a small bag. It could be in your vehicle, your EDC Bag, or 72 hour kit. These are larger and more comprehensive tools than whats found in your EDC or SERE Kit. You want to focus on sheltering devices like space blankets, small sleeping bags, mylar bivvy sacks, and heat sources for maintaining core body temps (like fire starting equipment). You will also want to have food stuffs like jerky/MRE main meals/granola bars. Items that don't require cooking. Have some water, a way to carry it, and a way to find or get more potable water on the move. Boiling is not the best option when your trying to get somewhere. So I would say to carry small purifying straws or water purification tablets. Small trauma kits would also go into this category. A small fixed blade knife and multi-tool could also serve you well. This kit is best designed to sustain you for a few days to get you to your desired location. You don't want to have to stop and build shelters, cook food or boil water. Your mission objective is to get to a safe place in the shortest amount of time. We will have a article published soon on "Defining the 72 hour kit" and this will go over the criteria for kits of this application.
Tier 3-72 Hour Kit and Beyond/BOB: In my opinion your BOB is not a 72 hour kit. A BOB is gear that you may need to survive in an unknown situation. Mainly because your having to "bug out" from your safe house and move away from danger. Could you use your BOB for a 72 hour kit? Sure, however I like to separate mine because my BOB is to extensive to carry everyday and have within an arms reach. This kit would also include larger firearms like rifles and more ammo, food acquiring equipment, cooking equipment like stoves, larger scale comm systems (HAM radios), major sheltering systems (down sleeping bags, tents, hammocks, and tarps), comprehensive medical kits, an environmental gear such as a change of clothing, larger buschcrafting tools like saws, pack-able axes, and larger knives. Again, this system is for the unknown, when you've had to leave your house, bug out location, or safe house and you may be placed in a survival situation Field craft skills are also a must for this scenario.
The water gets muddied on kit applications. Many people run systems together and this will leave you in a bad position. It's better to have yourself set up for success by developing systems around these types of scenarios. Also not that these kit items can be modular. Meaning that you don't need a flashlight for every tier. You will already have it on you and it can be used for that next tier. We will try and do a video on this subject in the future- if you guys are interested.