Kingfish strike hard and fast so choosing a quality line is especially important. You'll want to use 15 or 20 pound test monofilament which will stretch slightly to absorb the tension when a Kingfish hits. These light lines also cut through the water creating less bow in the line, therefore minimizing the drag.
In addition to a good monofilament, you'll want fluorocarbon line for creating leaders. Fluorocarbon practically disappears under water resulting in more bites. Seaguar Fluorocarbon is my preferred choice, though the Yo-Zuri H.D. Carbon Leader is also a popular choice amongst kingfishermen.