Madison Teachers, Inc. Solidarity Newsletter, via a kind Jeannie Kamholtz email (PDF):

Record keeping by an employee is important. Don’t wait for trouble to start before you begin to compile your own personnel records. Having good records is also very important, should you become involved in a grievance over your Contract rights or benefits, or in a matter involving discipline or dismissal. To enable the Union to provide the best possible protection and representation, every employee should maintain his/her own “personnel” records.
One’s file should contain such documents as: college transcripts, evaluations, accumulated sick leave and days used, direct deposit (wage) records, records of student disciplinary referrals, Wisconsin Retirement System (DETF) records, personal leave, documentation of honors and awards, notes on student accidents and confrontations with parents or administrators, copies of all correspondence with supervisor(s) and administrators, and for teachers – individual teacher contracts for each year, licenses, and teaching assignments by year with subjects taught.