I teach 3rd and keep a binder with lesson plans and related handouts. My week's plans are on two facing pages, tabbed with the week's dates. Behind it are all the handouts/answer keys for the week, organized by subject and tabbed Math, etc. I also add (on the lesson plans) any flipcharts I use on the ActivBoard or PowerPoints/printouts. I write in notes about whether I liked an activity or not.
When I taught middle school, I included any notes I wrote on the board. I did this by keeping my plans open on the computer during the day. Anytime I added/changed something, I modified the plans. These detailed notes really helped for the four years in middle school - I could refine notes, remember good ideas (
), what worked well, etc., and I could find everything easily. Also, I taught 4 sections of the same subject and it helped me to be sure they all got the same information.
I keep a separate, smaller binder for my hard copy of my gradebook, attendance, discipline forms, etc. Those things get discarded at the end of the year. The lesson plans become reference books.