The "skeptic" part covers the fact that my basic worldview is centered on the assumption that the world is rational, and all claims must be supported by evidence. I strongly believe that the rationality of the universe, in which sensory data can be used as the beginning of an inductive chain, is the one necessary postulate. (Without it, you have no basis for believing the sun will rise tomorrow, or that your dinner will not turn poisonous in your stomach; you're a solipsist. And the only thing a solipsist is good for is a laugh: Try sticking one at the wheel of a car, and telling him to drive towards a brick wall at a speed proportional to his disbelief in its objective reality.) Once we've accepted logic, logic itself dictates that we should support other claims using evidence and not postulate unnecessary entities. (Yay for Thomas of Occam!)
The "pantheist" part is because, while I don't see evidence for capital-G God, the independent entity that plays a role in the course of events or creates the world or whatever, I still don't think a materialist / rationalist worldview excludes a spirituality that finds beauty and divinity in the nature of the universe itself, and the other beings we share it with, and in ourselves.
And the "gnostic" part is because I think that beauty and divinity are things that can, and indeed must, be experienced directly by the individual sentient mind -- otherwise, the mind will be failing to serve its highest conceivable purpose (I apply the caveat "conceivable" because of course I don't believe in a creator or a teleological order), and beauty and divinity will themselves be lost, since the universe as a whole, lacking a mind, can't appreciate itself without the intervention of our sentient minds.
Which is all rather a mouthful, so having a simple two word phrase for it is nice. :-)