Don't expect your GPS to work indefinitely. When the power's out knowing where to bug out to is essential.
If you are trying to escape a disaster by driving towards a safer place then the most important thing is to ensure that you are actually moving in the right direction.
You definitely don’t want yourself speeding towards the town where the disaster hit. A road atlas is essential for your survival kit so that you know the shortest or safest route to the area where you can find refuge.