One area of the Humanities that I think everyone should study is philosophy. Philosophy courses will teach you how to carefully examine and construct arguments (as in, a point you would like to make, not a disagreement) and how to identify fallacies and weak points in arguments.
Even in science programs, philosophy is still important because it underpins all research methods. (Philosophy, for anyone who doesn't know, is comprised of four main areas: ethics, logic, metaphysics (the nature of the universe, nature of persons, etc.), and epistemology. Epistemology is the study of knowledge - how do we define knowledge, what can be known, etc. Consequently, epistemology underpins all research methods.)
I have a bachelor's and a master's degree in nursing, and I've taken three philosophy courses: one in general ethics and one in biomedical ethics in my bachelor's degree, and one in more general philosophy in master's degree. It was also a requirement to complete graduate ethics training prior to defending my thesis proposal. My experience has suggested to me that everyone should take at least two philosophy classes, because it can take some time to get your head around the concepts.