The starting point for understanding Christianity is the Scriptures. It is the Bible in all 66 books which tells the story that lies at the heart of the faith. The core essential here is that the Bible is the authority for the faith i.e. the authority of Scripture. The Bible is utterly reliable. It is completely trustworthy. It is inspired in that in some way, God oversaw the writing of its words so that through the words of Scripture he reveals himself to humanity. I would die for this notion.
Now how we formulate this is worthy of debate. Some argue for inerrancy, in that the Scriptures are utterly flawless in their original autographs according to authorial intent. Fair enough, I agree with this in principle; except that this tells us what the Bible is not and it is difficult to prove either way. It is also hard to formulate an understanding of an inerrant song (a Psalm), an inerrant parable etc. On the other hand, errancy cannot be applied to the Bible, as no 'error' has or can been proved; although skeptics love to leap on inconsistencies and argue for errancy. These cannot be driven home, as it all depends on authorial purpose and intent. Some argue for infallibility and again, I am personally happy with this, but the same issues apply.
There is also great debate as to whether the Bible is the word of God revealed or that through the words of the Bible God, the living Word, is revealed. Is the Bible objectively the Word of God or does it become the Word of God subjectively when the Spirit meets Word in its reading and proclamation. How is the Bible both the divine word and a human word, how does the divine work through and relate to the human? What is the relationship of OT and NT? Should we weight all parts of Scripture equally or give precedence in theological decision making to the NT or the Gospels, interpreting the OT through the lense of the Jesus of the Gospels? These are huge questions that Christians differ over.
All this is important to me, but in terms of life and death stuff, it is detail. The actual formulation of a theology of Scriptures authority and reliability becomes a good discussion but not the core issue I would die for. I would die for the belief that the Scriptures are authoritative, completely trustworthy and reliable, God-inspired, and the ultimate and defining source of our knowledge concerning God.
So for me the first essential reads something like: the Scriptures are God-inspired, utterly reliable, trustworthy, and the ultimate authority for knowledge of God's character and purposes. Through the Scriptures, I know God and I know how to live. Salvation is found through its message. I am not fussed how one philosophises or theologises this; as long as this is not threatened by the construct one comes up with.