What Should Be Included?

The short answer is anything and everything you can think of that you're going to need.

While the items you need are going to differ from the items I need because a bug out bag is a highly personal item, here's a list of what I keep in my bag:

         2 gallons of water. Yes, this is heavy. No, I don't want to get caught without water. In the event I have to strike out on foot and can't handle carrying this much water, I can ditch it at that point of time. I also keep a couple more gallon jugs of water next to my bug out bag that I'll throw in the truck if I'm able to take a vehicle.
         A butane torch lighter.
         A compass.
         A copy of your bug out plan.
         A couple candles.
         A handgun.
         A needle and thread.
         A rifle (figure out a way to attach it to the outside of the pack).
         A slingshot. This should be packed regardless of whether you pack a real gun in your kit. The slingshot can be used time and time again to kill small game and there's an almost endless supply of ammo everywhere you go. It's also quiet. You may not want to advertise where you at with the sound of a gunshot.
         Ammo for both guns and a handful of shot for the slingshot.
         As large of a supply as you can pack of any prescription medicine you'll need.
         Burn gel.
         Camping cookware.
         Can opener.
         Cash (spread out amongst bills, loose change and a handful or two of gold coins or diamonds).
         Back-up cell phone.
         Duct tape.
         Emergency blanket (reflective).
         Enough rations to last 3 days. Not enough to keep me full, but enough to get by until I can find another food source.
         Extra outfit of clothing.
         Extra pair of glasses and sunglasses.
         Fishing line and hooks.
         First aid manual.
         First-aid kit.
         Fixed-blade knife.
         Flares.
         Flashlight and a couple glow sticks. Buy sticks that last as long as possible.
         Flint and steel.
         Gauze.
         Geiger counter.
         Gloves.
         Identification (driver's license and Social Security card).
         Insect repellent.
         Leatherman-type knife.
         Maps of the area you plan on traveling to with alternate routes marked off.
         Medical records.
         Painkillers.
         Batteries.
         Passport.
         Radio.
         Raingear.
         Razor.
         Rope.
         Signal mirror.
         Sleeping bag.
         Small axe.
         Snake bite kit.
         Soap.
         Sun block.
         Sunglasses.
         Surgical kit.
         Survival book.
         Toothbrush and toothpaste.
         Water purification in the form of a Polar Pure Water Disinfectant Kit. I'm not affiliated with them in any way. The kit they sell uses iodine crystals to purify water poured through the bottle. It's good for up to 2,000 quarts of water. It's recently been called to my attention that this product is no longer on the market. You may still be able to find one for sale online, but you better move quickly. If you aren't able to get one, pack some water purification tablets. The only problem with these is they're good for one use only.
         Waterproof matches.
         Weapon(s) and ammo. You're going to want a way to defend yourself. A trusty handgun could mean the difference between life and death in a crisis situation.
         Whistle.
         Wire.

In addition to the items you have in the bag, there are a number of items you should keep near the bag, in case you have enough advance warning to where you're able to get in a vehicle and go.

Here's the rest of the stuff you should have on hand:

         A lantern with extra mantles.
         Extra ammo.
         Extra food.
         Food and water for pets.
         Machete.
         Mess kit.
         Propane canisters.
         Respirator masks.
         Rifle and ammo.
         Shells.
         Shotgun.
         Small stove.
         Small toys for the kids.
         Toilet paper.