In addition to backing up master regularly, keep offline copies of the sysdatabases, sysdevices, sysusages, sysloginroles, and syslogins system tables
Use the bcp utility described in the Utility Guide and store a printed copy of the contents of each system table. Create a printed copy by printing the output of:
select * from sysusages order by vstart select * from sysdatabases select * from sysdevices select * from sysloginroles select * from syslogins
If you have copies of these tables, and a hard-disk failure or other disaster makes your database unusable, you can use the recovery procedures described in System Administration Guide: Volume 2 > Restoring the System Databases.
Also keep copies of all data definition language (DDL) scripts for user objects.