Your local government will issue evacuation orders when a disaster is impending.  This will be communicated via local radio and television stations, or by local police and fire personnel going door to door, or by a reverse 911 phone call.

A disaster evacuation route and destination should be already planned and the tank already filled.

Take the following and there may be other thing that you would add:

Essential Supplies

• Checkbook, cash, and credit cards
• Car keys
• Map of area
• Cell phone and charger
• GPS
• Important Records Container
• Eyeglasses (with prescription if possible)
• Medical supplies including prescription medications
• Medical equipment - dentures, crutches, wheel chair, etc.
• Flashlight with extra batteries or a self generating flashlight
• Portable AM/FM radio with extra batteries
• First Aid Kit
• Bottled Water (1 gallon per person per day)
• Foods that do not require refrigeration or cooking
• Snacks
• A change of clothing for each
• Sleeping bag or blankets, pillow for each 
• Supplies for infant
• Toys for children

Papers to take with you

• Driver's license or personal identification for each person