This post is longer, in order to try to give pointers and resources to everyone in every stage of preparedness. Use what's useful, ignore the rest until you're ready for it.
If you're trying to figure how on earth to buy that extra food... case lot sales are going on right now, where items are often half the regular price. Some places- like the Bosch Kitchen Centers in Orem, Sandy, and on Highland Drive-- have Conference sales for long-storage items like wheat and honey. Plus the Home Storage Center has fantastic prices on wheat, beans, and more. You do not need to be a LDS church member to purchase items there.
Set aside a certain amount of money each month, and use it. For more ideas, see this Conference talk by Elder Featherstone.
Do you need your 3-month supply? Do you have that in place and are ready to move on to building your long-term ("year") supply? Do you have long-term storage but just need to get organized or fill in some gaps?
To build a three-month supply, you and your family decide on 2 weeks of meals that they like. Figure how much of each food item you need for that two weeks, and multiply by 6. This gives you three months! Remember that what you already have counts towards this amount. I have a series of blog posts on a three-month supply, too.
To build long-term storage, first figure how much you need. I've compiledinformation about that, here. There's even more, here. It really is not as overwhelming as it sounds. You'll likely spend as much money on the three-month supply as you will the entire rest of the year's worth; basics are cheap. Last time I ran numbers, getting that 9-months-more of storage was under $250 per adult, and less for children. (See the link earlier in this paragraph for children's quantities.) There is a useful spreadsheet here; feel free to change quantities for the different grains, as long as the total remains 300-400 lbs.
"Food storage is often characterized by worldly critics as eccentric — just steps away from building a nuclear bomb shelter under your house and stocking it with guns, ammo and dehydrated rations.
If you have held back from applying your imagination and effort to storing some necessities for a rainy day, let me ask this: Have you ever saved for your child’s education? Have you ever hurried to buy airline tickets a month in advance of Christmas, because you knew that available seats would disappear if you waited longer?
Do you pay for health, disability, auto, or life insurance, even though you are healthy and able, you don’t plan to be in an auto accident, and you are indeed alive and well? Then you are a candidate for food storage and a provident lifestyle.
Even if you never use your food storage for an emergency if you store what you eat and eat what you store and you will always be eating at last year’s prices. You will never have to pay full price for food in the future. Even food goes on sale. It is really that simple. Who wouldn’t love that?" -Carolyn Nicolaysen
President Monson said, one year ago, "We should remember that the best storehouse system would be for every family in the Church to have a supply of food, clothing, and, where possible, other necessities of life... Are we prepared for the emergencies in our lives? Are our skills perfected? Do we live providently? Do we have our reserve supply on hand? Are we obedient to the commandments of God? Are we responsive to the teachings of prophets? Are we prepared to give of our substance to the poor, the needy? Are we square with the Lord?
"We live in turbulent times. Often the future is unknown; therefore, it behooves us to prepare for uncertainties. When the time for decision arrives, the time for preparation is past."
("Are We Prepared?", Sept. 2014 Ensign magazine)
"It requires faith even among the Latter-day Saints to believe the revelations of God, and to prepare themselves for those things which await the world… And what I wish to say to the Elders and to the Latter-day Saints is—Have we faith in God and in his revelations? Have we faith in our own religion? Have we faith in Jesus Christ? Have we faith in the words of the Prophets?...
If we have faith in these things, then we certainly should prepare ourselves for the fulfillment of them.'
-Wilford Woodruff, "The Parable of the Ten Virgins"