In my never-ending quest to reduce my footprint on this planet I decided early on that it was important to only eat food that was in season in the region I live. This is important as it means whatever you're eating isn't being transported extravagant distances to get to your grocery store before it reaches your plate. Basically the premise is that your food has less 'food miles' (less pollution, greenhouse gases, etc).
Also if the food you eat comes from your region you're more likely to be able to track down the producer or at least understand the way in which your food is produced because you become more interested in learning about this and more connected with the people that produce your food. In turn, you might even care how it is produced and ensure people have appropriate working conditions and produce food in a manner that in itself might be a lighter footprint (for example, organic practices, etc).
What I really need is a guide to what is in season that I can carry around me when I am buying my produce and then a recipe book that can give me recipes for the relevant season. I have come across a few these cook books in my local library, mostly with organic cooking or something along those lines in their title. If you are borrowing such books, make sure they are published in Australia (or the country you are in), as it isn't relevant to be looking at an English book. Their growing climate is different, soils are different and therefore the produce that is available to the English in the various seasons are likely to be different to what is available in your region.
The what is in season, as a store guide, has eluded me though. Well a quick and easy reference type one for my region. The best I can come up with at present is something along the lines of the Vegie Guide on the ABC Gardening Show's website. This shows you what to plant in your region according to the season. The only issue is this guide is for planting of produce not for eating. Thus, there is some calculation required because obviously what is ready for planting isn't ready for eating....a lag time some might say.
I will one day get off my butt and find something appropriate or develop it myself.