Stage Managers are generally aware that their prompt book needs to stay in the theatre at all times in case the unthinkable happens and someone else has to fill in. However, it is not just the calling of the show that will need to be covered should you get hit by that mythical bus! Make sure that there is no place in the building for which you have the only key--this includes your desk, any safes, all doors. Make sure that any security, phone access, copy or lockbox codes are posted somewhere. In general, take a day or two of performance and notice every action you do. Make sure that there is some way for a substitute to understand and do the same.
