One of the first steps anyone who wants to survive needs to learn is that you can't live the same way you did beforehand. Your reliance on processed foods never seems to be so apparent as when you try and live without them. The single hardest thing for me to give up was the Jack in the Box 2/99 cent tacos.
Depending on the space available, you may not have to alter too much in your eating habits. Since our experiment is only on 0.12 acres, we needed to modify our diet quite a bit to make this work. Thankfully we've gotten into the habit of eating more vegetables and trying to do without a lot of the "luxury" foods. I don't think we've eaten peanut butter in 6 months, which is a pretty amazing feat with 3 young kids. We've gone without buying bread in several months, making a loaf at home should we find ourselves wanting bread. We still need to cut back on our cheese consumption, as our little plot of land does not give us room or zoning for dairy animals. That proves to be a bit tougher than the peanut butter.
By all means, you do not need to become a vegetarian, or start shopping at the organic sections of the grocery store. You just need to re-evaluate what you are willing to do to survive and thrive off the commercial food grid. It's a slow process at this time in history, so take your time, weed out some of the junk and learn to eat a few new things. Buying a vegetarian cookbook is a good way to introduce new homegrowable produce to your family. Try something different from the local farmer's market or butcher shop. Find out what you can eat when the normal foods in your life may not be available, and introduce it slowly into your lifestyle. This way when you are pushed into that more basic lifestyle, you will not experience the shock of a hoarder. Practice makes permanent, so develop your good habits now.