What you do before you leave depends upon two things: How prepared you are and how much time you have.
These two factors will govern whether you get out with nothing or escape with sufficient items to keep you and your family comfortable while away from home.
If you prepare in advance, you will be able to recover more quickly. You will not only have enough to see you through this rough time, but sufficient documents to make it easier for you to get shelter, process an insurance claim and deal with other government bureaucracy resources that will be around when a fire sweep through.
In case any of your personal documents don’t make it out with you, replacements can be ordered through: http://www.usa.gov/Citizen/Topics/Family- Issues/Vital-Docs.shtml