Here is my somewhat generalization of the preps as far as food goes. Of course their will be carryover, and should be diversity in your preps.
2 weeks- Pre cooked, ready to eat food will probably be the easiest. This means canned food and MREs. Stuff that doesn't need to be cooked or hydrated, just heated. Also non perishables such as peanut butter and such.
1 month- Everything from the 2 week mark + prepackaged emergency meals. Stuff like mountain house, ramen noodles, and those emergency buckets.
3 months- Everything listed before, just more of it. Plus bulk dry items stored accordingly. Rice, beans etc...
1 year- Everything listed before... just more of it. Things that would be additions that should not be overlooked is salt, seasonings, cooking oil, and even multivitamins.
Indefinite- I hope you're ready to start growing your own food.
Water storage, collection and purification is a whole other story.
It really does not take much money to put away a bare minimum of food for 2 weeks if you are not a picky eater. A trip to Costco will cover that and more in most circumstances. A 20lb bag of rice, 2 cases of ramen, a case of canned tuna, a case of spam or Vienna sausage, a few cases of bottled water and a 2 pack of those big jars of peanut butter may not be the most nutritious food stores.... but they are enough to live on for most emergencies.