I strongly agree with his first two suggestions. In today's world, we receive copious amounts of information in the form of statistics, such as information about the environment, elections, and your health. On the whole, however, we have low levels of understanding of statistics. You would be much better at understanding all the statistical information you get if you took a basic statistics course while in college.
Economics is also a good choice for the analytical tools it provides. Learning to view the world through the lens of economics is good training for your mind. Plus, it will help you better understand economists when you hear them debating important issues of the day, such as debates over economic stimulus and tax cuts.
Psychology was an interesting choice for an economist. But, I like Mankiw's explanation:
For many purposes, [economics] is useful. But it is only one way to view human behavior. A bit of psychology is a useful antidote to an excess of classical economics. It reveals flaws in human rationality, including your own.You may be wondering why I haven't suggested that you take the class that I have taught the most--US Government & Politics. I do think you should take that course, but not for your personal benefit--for society's benefit. Since we live under a political system that requires the participation of its citizens, everyone benefits when our citizens are well educated and have a firm understanding of our government and politics.
What courses do you think best prepare students for life in today's world?
Read all of Mankiw's editorial here.