Hi Donald:
Gosh, no one is expected to spew out their lifetime of knowledge in a moments notice! Sheesh!
A journal can be what ever you want it to be. A chronological record; reflections of daily classes; valuale tidbits that "came to you" during the lesson; observations of stuednt behavior and your handling of these, to name just a few. What's helpful is looking over notations later on, whether that's weeks, months, or years because that'll reflect and reveal growth, maturity, and help identify strengths.
Also, remember, you're probably following a set curriculum with course objectives and student learning outcomes. So as long as you cover those (in your own special way), the stuednts will get what they need.
Regards, Barry