Just wanting to give some advice from the standpoint of someone who worked at a cell phone call center during Katrina.
I know saving cell battery seems important but as it goes on with no power more and more people are going to try and use their phones before the phones die. Cell towers can only hold so many people at a time and if you wait until them the chances you will make it through is super small.
Also as it gets worse more people will try to reach loved ones and that takes slots too. Basically what I'm saying is if you have service use it while you can. Get info about where you go if you need to leave and make a plan now. Email that plan to everyone you can right now.
If your cell dies, the slots get taken, or the tower goes down *which is the most likely scenario* your phone is going to be worthless.
Trust me so many people waited so long to get a plan they weren't able to tell any one and that caused a lot of families to not know the status of each other for months.