We need to secure supply staff, but we don’t know what the subject will be. What should I do?

Select 'Other' under the subjects drop-down list and then in the 'Job Description for the Supply Staff' box, write something along the lines of: "The subjects have not been determined yet. We will try to adapt subjects to suit your skills and abilities but ask that you also be flexible in this". This way, the supply staff will be prepared for mixed subjects over the course of the day and you will be sure to get a supply staff who is flexible and open to these sorts of jobs.