
Store water! I can't say it more directly. Before you do anything else in your preparations, get and store some water.
How much water? As much as you can. In my opion, at least 1 gallon per person per day, more if you can. When you consider drinking, cooking, cleaning and sanitation, 2 to 4 gallons per day would be even better.
You can start off easy and just buy a case of water in either 1/2 liter (500 ml) or 3/4 liter (750 ml) bottles - these are the common "sports bottles" that you see everywhere. It is a good idea to store a couple case of these smaller bottles even if you have water in larger containers too. The small bottles are easier to transport if you need to leave your home in an emergency. If you are buying your water pre-packaged, consider some larger containers as well such as 1 gallon PET bottles (PET is that clear plastic that is clear like glass). I also recommend some of the 2.5 gallon plastic water bottles for storage. However if you buy these get them by the case (2 2.5 gallon containers per box). The box will protect them and help them last longer. These containers are made from HDPE which tends to crack and leak over time. In my experience they will last about 2 years in the case.
You don't have to purchase pre-packaged water of course. Tap water is cheaper. Save 2 liter soda bottles, rinse them and fill them with water for storage. They are easily transportable and reusing is a cheap option.
Or if your budget will allow buy some some larger containers. I like the 7 gallon Aqua-tainer brand. They are very durable, though when they are full they will be heavy. Best to store for use at home, though if need be you can move them in a car or truck. They have a nice built-in spigot, too.
Lastly, do you need to treat your stored water? I do not. My municipal water system uses chlorine and there is plenty in the water already. Now, if the municipal water system is impaired or impacted in a disaster but it is still working, you will definitely want to treat, filter and / or boil your water before use, just to be on the safe side.
So, don't forget to store that water. You may never need it, but if you do - then you really do!
That's my thought on prep.