Here’s a word from John Frame about sola Scriptura in writing about the Regulative Principle of worship.
Nobody has ever claimed that Scripture is sufficient for every detail of life. Scripture is sufficient, not as an encyclopedia of laws or facts, but as the Word of God. To say that Scripture is sufficient (in public worship or elsewhere) is simply to say that Scripture contains all the divine words that we need. Scripture is sufficient for the civil magistrate, not by telling him exactly how much to collect in taxes, but in giving him all the divine norms he needs to make his decisions. [Frame is responding to T. David Gordon in his reference to taxation.]
People violate sola Scriptura, not by asserting that there are truths to be found outside of Scripture, but by claiming that there are extra-biblical words that have the same authority as Scripture, or higher. Those who believe in sola Scriptura hold that no extra-Scriptural words have divine authority, and therefore supreme authority. People violate the principle when they claim that their ideas, their norms, their political philosophy, their view of taxation, etc., have authority equal to or greater than Scripture.*