I want to convey it with a single word that I'm a rational person who values the understanding of objective reality rather than superstitious nonsense. Ideally, it would fit in the slot normally reserved for "religion" on surveys, military dog-tags and such.
"Atheism" is too reactive. As Richard Dawkins points out, practically everyone is an "a-Thor-ist" or an "a-FlyingSpaghettiMonster-ist". One shouldn't have to specify every possible type of nonsense which one does not believe. Atheism has such a bad public image too. It's been associated with Communism, Stalin, Hitler, etc. I'd rather have a word which is so obviously sensible that vilifying it would be next to impossible.
"Skepticism" is closer, but similarly reactive and negative. The skeptics of ancient Greece were not socially acceptable.
"Naturalism" (as opposed to supernaturalism) might have worked if there weren't already so many different meanings for the word. In many languages other than English, a literal translation would mean the same as "nudism". Not very respectable.
"Realism", "rationalism", and "materialism" also suffer from semantic overload, mostly from the liberal arts camp.
I'm thinking that the Greek and the Latin may already have run out of good root words for us to re-use for this purpose. What do other languages have in their stock to describe someone who eschews nonsense and laughs at superstition?