My list has some obvious tools that are not part of most undergraduate curricula but are I think essential. For instance, knowledge of the principles of system thinking is necessary for understanding the complexities of modern economics, politics and culture, much less the world of biological ecology. The ideas of iteration, logical construction and structured organization found in computer programming are important for understanding modern technology and basic reasoning. Methods of approaching large data sets and making conclusions under uncertainty are also very useful.
But other less obvious thinking tools would also come out of my list. When a person learns a coordinated physical activity, they have a kinesthetic analogy from which to draw when thinking about a problem. The experience of creating a physical object with their hands may help students see ways to improve their physical environment. Having created a new idea will make it easier to create another one. Living in a foreign culture might help break the bonds of ethnocentric thinking. Doing community service could help develop empathy and the ability to see the world through others’ eyes.
I have often said that college (even life) is process of collecting as many problem solving methods as possible. Classical liberal education sells itself as the best way to develop critical thinking tools. Let’s expand and modernize the definition of a liberal education.