Make sure that any container you use for water storage is food grade and clean.
New 55 gallon drums cost $40-45. They are a great way to store the bulk of your water. There are pumps available that are made to fit these barrels.
2 liter bottles are easy to move and to store in key places around the house, like under the bathroom or kitchen sink. It is much easier to use a small bottle at the sink than it is to run to a large barrel somewhere else in your home.
If you have to go get more water from somewhere like a lake or a water truck, containers that are 5 gallons or less will come in handy. Since you may have to carry these, consider full weight when buying. Water weighs about 8 lbs per gallon. If you have a wagon or a wheelbarrow this will help in the transporting of your water to and from your home.
If you have room for a water tank you can easily store 500 gallons in an area 4' square and the cost could be half of what you might spend on 55 gallon drums. One manufacturer is Rotational Molding of Utah. You might be able to find a manufacturer near you so you don't have to pay high freight charges.