Neko-Chan, I have long had an
academic interest in this question. For awhile, I lived in the country and grew nearly everything I ate. I worked for my farmer neighbors for monetary income. That was many years ago.
I make the little joke that these days, I grow enuf to sell - then, use that money to buy apples and broccoli thru the winter. It is kind of crazy but comes fairly close to being true. After having it from the garden nearly continuously for 7 or 8 months out of the year, we even buy bok choy in the winter. See, I really am crazy

!
Always grow more than you think you need rather than less. You may be able to sell that produce or make friends by giving it away. The article linked by Ridgerunner has John Jeavons cited on the 1st page. Jeavons talks about using 60% of what you grow to
feed your compost pile! I think that makes a world of sense even if I don't do that

. Anyway, your soil is always hungry so, feed it

.
Here is another resource to look at that talks about
yield from your garden:
Purdue, Intensive Gardening.
You didn't quite ask this question but I have used the
magic number of 125 to talk about annual food needs for a single person. You can multiply those 125 pounds times the number of people in the household for each food group. I talk about the 125 pounds as a "spud unit" and start off with that all-important food group. The number has to be kind of hammered into the other categories but it is all kind of generally true. I've looked at a number of government resources and added up what we are told that the Average American eats. I don't suppose that an Average Australian would be that much different:
Annual Food Consumption
125# potatoes (a "spud")
125# red meat
125# other meat (inc. fish), eggs, & cheese
125# wheat flour
125# sugar
125# other foods (fats & oils, rice, nuts, coffee etc.)
(2)125# vegetables
(2)125# fruits
(4)125# milk
You can see that besides the potatoes, you need "other vegetables" times 2 and fruit 2 times 125#. Milk is something of a separate category but still should be included.
Steve