So you want to build a bug out bag. No simple pre-assembled, commercially-available kits will do for you. (And for the record, I recommend building your own. You'll have complete freedom of choice for every item in the bag, ensuring its quality, usefulness, and most importantly, that you know it's even there in the first place.)
How to proceed?
Choosing the pack
You can use an old school or camping backpack, or buy a new one. I originally co-opted my old law school backpack, a Jansport, for this new duty. (I've since acquired more than it can hold, and upgraded to a 5.11 Tactical 72 RUSH pack.) I emptied it, put it through the washer with a tiny bit of soap, and hung it to dry in the shower overnight. The next day, it was ready to use.
If you are buying a bag new instead of using one on hand, take some care in selecting it. I would not recommend a duffel bag because of the uneven weight distribution. You need to be able to carry this pack hands-free for long distances if necessary. It needs to fit well -- if you are a small person, buy a mammoth-sized pack at your own peril. Also consider internal organization, such as pockets and dividers, and external organization, such as MOLLE and PALS attachment points that are available on tactical bags. Ask yourself if you want the bag to have a pouch for a hydration bladder like a CamelBak.
My pack presently weighs in at a doable 19 pounds. (I’m such a girl.) The general guideline for the amount of weight that you should carry in your pack for a multiday trip is up to 25 percent of your body weight. Obviously this varies with your size, weight, and physical condition. If you are older, have back problems, are not in good health, or for other reasons cannot carry a heavy pack, I would recommend that you look at assembling a smaller, lighter bag using a “lumbar pack” available from many outdoor equipment retailers. This is basically a larger, more rugged fanny pack. The obvious trade-off for the lighter size is that you will have to carry only the barest essentials, so choose your gear wisely. Regardless of the size and weight of your pack I recommend that you train with it -- try walking a mile in it and see how you hold up.
The conventional wisdom for a pack such as this is that it needs to supply all your needs for three days. For example, if an earthquake strikes, or there is a chemical spill near your home, this is a bag that you would grab from your closet or the trunk of your car in ten seconds while evacuating your home that would have everything you needed to get by for three days -- after which time presumably you will have been allowed to return home, or will have found refuge at a local shelter or with family and friends who are still in their homes. For myself, I carry more than this, as I anticipate that it will take at least a week if I have to hike home to my family should the major urban center where I live become uninhabitable.
As will quickly become apparent from perusing the list below, your pack will be a treasure trove of very valuable items, some expensive, and some inexpensive but still very sensitive. Your personal identification, any firearms, and the emergency cash are all items that any thief would be glad to have. You will have to make a personal choice about how and when to keep your bag with you. If you keep it in the trunk of your car, you will have it with or near you at nearly all times, which ensures that you will have it whenever the need arises. The trade off is that a thief who steals your car will also have the bag now and you will not only face the inconvenience of a stolen car but also identity theft.
Packing your bag
The list below looks extremely long, but in fact, most of these items are in my bag. Many of them take up very little space especially when compared to their utility or the degree of comfort they will offer in the event of an emergency.
Some simple guidelines will help you to pack your bag in an efficient manner. Try to keep the center of gravity close to your back, and not too high in the pack unless you are not going to encounter any steep or rough terrain. Frequently-accessed items, as long as they are not too large, go in outer pockets. For more detailed information on loading your pack depending upon your sex or the type of terrain, I suggest you consult The Backpacker's Field Manual by Rick Curtis.
Most items need to be sealed in plastic bags or Aloksaks to ensure they are kept dry in inclement weather; use your common sense as to what will not need to be waterproofed. Aside from the waterproofing issue, the plastic bags are useful for grouping categories of items together for organization and ease of access and for tight and efficient use of space, both inside the plastic bag and out of it.
Building in redundancy
For very critical items such as water, fire, and light, I recommend including redundant sources. This is so that if one tool breaks, you have a backup or alternate ready to go. The truly hard-core preparedness types use the acronym "PACE," which means Primary-Alternate-Contingency-Emergency, or having in mind four different ways to accomplish a task at all times. You may also see the phrase "three is two, two is one, one is none." Same idea.
Read the manual
If you carry any technically advanced or potentially hazardous items such as a camp stove, personal protection device, Leatherman tool, or any item whose operation and use is not intuitive for a five-year-old, make sure that you learn to operate the item immediately upon purchase and BEFORE putting it in your bag. An emergency is not the time to try and figure out how to use the thing.
There are several items on this list that will require you to exercise your own independent moral judgment. The two major areas are, first, the issue of self-protection, where you will have to decide what type of weapon to carry and, second, for women, whether to carry a dose of Plan B to prevent pregnancy in the case of sexual assault. If you choose to do so, you should know that Plan B is available without a prescription at your local pharmacy, although you may need to ask the pharmacist for it. It is not a good idea to attempt to purchase it at the last minute because the local pharmacist may choose to exercise their right of conscience in refusing to dispense the drug, and you will have to find another source that will sell it to you.
If you choose to carry a firearm, please ensure that you obey all local and federal laws while doing so and are sufficiently trained and rehearsed in the safe and accurate operation of the gun. I do NOT recommend deciding not to carry any protection at all. You need to be able to defend yourself. How you do that is up to you.
This list is not exhaustive. Use your own sense when constructing your bag.
Emergency rations and ready-to-eat food items, 3 days
Optional: Camp stove or Jetboil personal cooking system, with fuel canister (will provide approximately 90 minutes of cooking time); for families, consider a Helios cooking system.
Optional: Fuel for campstove
Optional: long-term storage multivitamins, such as SuperSpectrim
Optional: Lifetabs or other survival/energy tabs
Emergency water packs, 3 days, plus extra if you have pets (see below)
Katadyn Ex-Stream XR personal water filter
Micropur water purification tablets
Emergency tube tent or tarp
Tennis shoes or hiking boots
Socks, 3 pair
Underwear, 3 pair
crushable hat with brim, such as a boonie hat
Optional: one pair of jeans or other comfortable pants; one cotton t-shirt
LED headlamp, batteries stored separately
Small flashlight, batteries stored separately
Light sticks, 3
Small toothbrush and toothpaste
Two large trash bags, to dispose of waste
Comb or brush
Mini rolls of toilet paper
Small microfiber towel, like Packtowl
Safety - choose at least one
Firearm with appropriate JHP (jacketed hollow point) ammunition, concealment holster, extra magazines, and small cleaning kit
Knife, fixed blade or folder with locking blade
Pepper (OC) spray
Survival Kit - I recommend the Doug Ritter version from Adventure Medical Kits.
Leatherman tool or utility knife (look for a blade at least 2 1/2 inches long)
100’ 550-lb paracord
Small waterproof notebook, such as Rite in the Rain, and pen or pencil
Detailed map of your local area
Detailed map of the route from your home to any “bug out” location, such as family in another city; with primary and alternate routes highlighted in different colors
$100 in cash, small bills only, plus roll of coins if desired
Photocopies of your ID, birth certificate, social security card, health insurance card
List of phone numbers and addresses of family, relatives, and friends (do not rely on your cell phone to provide this information; it may be dead or you may not have it with you)
Passport (or photocopy thereof)
Fire - choose two or three methods of firestarting
Kindling, such as Wetfire, cotton balls soaked in vaseline, or small bag of cotton-fiber dryer lint
First aid kit sufficient to deal with both "boo boos" and "trauma"
Supply of any critical prescription medications -- pack extra in case you are gone longer than three days
N95 or N100 respirator masks, 3 (one per day) (for dust and smoke)
Lip balm w/SPF
Insect repellent towelettes
Optional: emergency surgical kit, CPR kit
Pets (per pet)
Food, 3 days’ worth, sealed in vacuum bags if possible
Water (see above)
Collapsible plastic food and water bowls
Copies of their most recent rabies shot and city license, if required
One dose of Advantage or other flea and worm preventative
Nukalert personal radiation meter
Potassium iodide or potassium iodate tablets (thyroid radiation blocker) (for nuclear incidents)
N95 or N100 respirator masks, 3 (one per day) (for pandemics)
NBC-rated gas mask (for nuclear, chemical, biological attacks)
Feminine hygiene products
Optional: Plan B, one dose, in case of sexual assault
Travel-size Bible, Torah, Qu’ran, etc.
Pack of playing cards