Sustainability through gardening
Believe it or not, putting your backyard to good use is one of the most significant ways you can contribute to the sustainable future of our society. Your backyard will never be as productive on a per hectare basis as a well run farm, but you wouldn't want to have all that poison floating around the suburbs anyway. Backyard food production allows you to pursue a completely different strategy. Rather than a chemical enforced monoculture reliant upon heavy machinery, fossil fuels, dams, barbed wire and elaborate transport infrastructure, you can create a diverse and productive ecosystem right where the fruits of your labour are to be consumed. You can take advantage of unused land, human labour and wasted water. You can produce healthier food.... A garden producing a variety of fruits and vegetables will support a far higher biodiversity than a neat lawn.
Unfortunately, one of the mistakes people often make is try to grow unsuitable plants. They end up putting in a lot of labour and getting very little reward. Luckily there are plenty of crops available that are easy to grow. Some are even considered a weed or a pest. The most important advice I can give you is to get seed from your local area. Talk to your neighbours about what grows well. Selecting a local variety is far more important than trying to choose the right time to plant, the right level of shade, the right soil moisture etc. You just aren't told this because it doesn't sell seed packets.
Look around at what everyone else is growing, however when it comes to fruit trees it is not necessarily best to go with what is grown everywhere as this is determined just as much by cultural factors as it is by suitability to the environment. Plus, if a fruit is grown everywhere there are probably a lot of pests around feeding off it.
Another trap people fall into is listening to the experts and trying to grow 'heirloom' vegetables which require a bit of skill and planning. These are great for when you have some experience, but when you are starting out just keep asking around for things that are easy to grow.
For those of you in Brisbane, I will share some of my personal experiences. The following crops are listed in order of the ease with which they can be grown. I have fairly heavy clay soil.
Finally, don't be led to believe that you need to spend a lot of money to use water sustainably.
Photo of two critters I busted mating on my fig leaf (and eating it too).