I like to keep a list of real-life examples of units, so when I come across metric dimensions, I can recall (or state for others) a suitable comparison point. I have some decent ones for area (at least for someone who lives in southern California, United States), but am not comfortable with the examples for volume and weight.
Do others here on this list have some good real-life examples? You can see what I have, on this pdf: http://www.paulrittman.com/Metric.pdf
