Ken Samples does a great job here explaining what sola Scriptura (Scripture alone) does not mean.
1) Sola Scriptura does not mean that other authorities besides Scripture can’t be appropriately recognized by the church. Creeds, tradition, consensus of the church, and human reason all provide valuable judgment. However, they are subordinate to the supreme and final authority of Scripture.
2) Sola Scriptura does not repudiate the usefulness of tradition in particular as a subordinate norm in theology. It may be quite acceptable to allow tradition to play a secondary (or derivative) role in the formulation of doctrine (for example, the ecumenical creeds of Christendom).
3) Sola Scriptura does not repudiate the church fathers or church history overall. The great leaders and teachers in the history of the church have provided invaluable instruction in theology, but (as those same individuals have often remarked) their views must be appropriately evaluated in light of the supreme theological norm – Scripture. Examples from church history can still provide a secondary form of spiritual guidance for Christians.
4) Sola Scriptura does not mean that all truth is found in the Bible or can only be found there. Certainly all truth is indeed God’s truth. Information found outside Scripture (in general revelation, tradition, and so forth) can be genuinely true and may actually correct misunderstandings of Scripture. However, alleged truths that contradict Scripture are not genuinely true.
5) Sola Scriptura does not deny that the Word of God was initially in oral form. When the apostles were living, they spoke and wrote with divine authority as the Holy Spirit worked through them. However, upon their deaths, the only reliable and accessible apostolic source is found in the Bible.
It is indeed helpful for us, when thinking of the Reformation cry “Scripture alone!” to remember what it does not mean. Samples’ list above is a good one to remember in this area. If you’re interested, the list was taken from Kenneth Samples, A World of Difference, p. 120.