When starting a bug-out bag, I always recommend people look at the information on www.ready.gov and www.getprepared.gc.ca. Especially their gear lists. They're government sponsored websites which explain the bare minimums one is expected to have for an emergency situation. They're a great place to start for the novice interested in being better prepared.

The only area I kinda differ with them is on the issue of water. Ready.gov recommends one gallon per person per day, which is perfectly appropriate. However, if you're trying to make a backpack or duffel bag style BOB that you can easily carry, that's simply too much weight (25+ lbs in water alone!). For individual kits where I don't have the support of a vehicle, I'll carry less water out of necessity. However, I'll also make sure to have a few methods of water purification in the kit.

Also worth stressing is that you should have copies of all your important paperwork, as well as all the paperwork you would need to start a new life in a different area. That's where a lot of people get screwed. They end up having to leave their old life behind with no documentation proving who they are, what they owned, that they had insurance, that they were qualified for a job, ect.

Finally, I also think it's especially important for each person to have an individual bug-out bag, even if you do have an overall family bag. Children too should have some gear on them, even if it's just some basic food, water, and toys. The simplest reason for that is the whole, "never have all your eggs in one basket" line. If you've only got one big bag and something happens to it, you're screwed. With a bunch of little bags you might at least be able to salvage something. Plus you never know if you might somehow get separated due to some secondary event that is out of your control.