The context of what "alone" means is necessary.
If I say "I only love my wife" do I mean that my wife is the only person who I have any love for? That I don't love my children, my parents, my siblings, my friends, my neighbors, or that I don't love the Lord? Of course not. It would mean that I am faithful to my wife and that I am not chasing after other women. The "only" here is contextually grounded in the spousal relationship.
Likewise the historic definition of the "alone" in Scripture alone is that only Scripture can be the infallible rule of faith and practice. That does not mean that we reject the fathers, the creeds, and the historic traditions of the Church; it means that Christian faith and practice is chiefly guided by the rule of Scripture, and that which is at odds with Scripture are overruled by Scripture. Thus the command that we believe in and worship only one God means that we cannot believe in and worship any other god; that should seem somewhat obvious, but if someone out there starts preaching that there are many gods, we can point to Scripture and say, "No, we confess there is only one God and He alone do we worship." And that, precisely, is also how the historic Creeds came about, precisely by articulating the faith as we have received it from the beginning. The Creeds do not introduce novel doctrines, but affirm and articulate the true faith as we have received it from the beginning. Thus the Creeds are dependent upon Scripture, upon the unfailing rule of faith as received and confessed from the beginning as we see it witnessed to in the writings which have been received as Sacred Scripture.
"But the Bible is tradition", yes it is. The Canon is most definitely a tradition of the Church, and so our acceptance of the Bible is a subscribing to the tradition of the Church--there's nothing wrong with tradition, and the historic position of the Reformation Churches was never to reject or abhor the received traditions of the Church. But what the Reformation did argue was that novel teachings, practices, and traditions which were in conflict with the ancient faith and which were in conflict with the received word of God in Scripture are problematic, and that if we must choose between what those in positions of ecclesiastical authority say and what the Scriptures says, the Christian as an individual and the Church as a whole must choose Scripture over anything novel and contradictory to the apostolic faith.
It is a methodology of making address and rebuke to teachings and practices which obfuscate the truth of the Gospel, in order to preserve the Gospel as the chief article of Christian faith; that the Church faithfully preaches the word which she has been entrusted to preach from Christ her Lord.
In the centuries since the Reformation some Protestants and some Protestant groups have come to grossly misunderstand what Sola Scriptura means in its proper context. This is not the fault of Sola Scriptura, but rather the fault of those who are unwilling to understand the proper history and context. Sola Scriptura only makes sense in the context of historical Christianity, removed from that context and it largely becomes meaningless, and little more than justification for some to engage in carte blanche DIY religion.
-CryptoLutheran