So, what to plant? I think the mistake that I see most often is that people get all fired up about planting tomatoes and herbs and the like, which is good--but not at the cost of neglecting staples. Many assume that major staple foods like rice and wheat will be available if expensive but garden crops like the above will not. This is not what history suggests: Actually the basic staples are the first thing to go. Again, we've already seen this with rice, and to some degree both corn and wheat. In the age we live in, these common and traded commodites are also much more vulnerable to market manipulation--whereas other crops are not. This is a risk as well. Also, we face competion from the biofuels market for things to eat--this as well has caused a great deal of price pressure on basic staple crops. I do not see any of these trends easing any time soon.
The great difficulty is that the majority of staples are difficult to grow in a garden setting. They tend to be best cultivated in large land holdings and with mechanized cultivation methods. Growing wheat in a small home garden is a near pointless exercise and a waste of space. While one can grow beans, or chickpeas, or even corn and potatoes--and certainly I grow a lot of sweet potatoes--yields beyond what basic subsistance requires are often difficult to come by. Few options exist, and careful research is bound to be important. Ask, what is it that you're going to eat every day? It's not going to be lettuce. What will be the backbone of your homestead?