I am calculating an "average" of about 60 people per house - an average daily intake of food for males needs to equal about 3000 calories and for females needs to be slightly lower at 2500 calories. For someone to store that many calories per person for that many people, you would need to have something like a small warehouse to hold it all - an almost impossible task, but, it can still be done.
My recommendation would be more along the lines of what Blob suggested - instead of having just four places for the food to be stored (enough food for 300 people), setup more safe-zones for the food storage.
Peanut-butter and honey stores well, both have great calorie counts and then store crackers (instead of bread) to spread the PB-n-H on. 1200 people would get real tired of that quickly. Another great calorie food would be canned ham, canned tuna, canned salmon, mix with some sauces (MiracleWhip) and spread on crackers.
Case-lots of PowerBars (about 300 calorie per bar) might be needed to suppliment the energy needs of the masses, case-lots of powder'd Gatoraid stores well, powder'd icedtea stores well, and water can be stored in 10 gallon jugs and placed on coolers. A single 10 gallon jug would be needed per person just to drink for a week, how do you plan to store that much water?
Something that might be a better choice is to have the members of the co-op store their own food/drink based on averages, have a weekly inventory-count of the stocks to make sure that each member is doing their part equally.