What are you buying from the bargain bin? I know that prepared foods don't work well with most diets. They tend to be high in fat (ouch) and high in salt. Unfortunately, you really have to cook on most diets, instead of just open a can.

I try to do salads, and a lot of fruit. I buy what's in season if possible, and go to farmers' markets. They aren't always cheaper but the quality is usually better so I waste less.