You should maybe start off with teaching them something about security, then touch on security a bit, and end with a session on security.
Just kidding, but it always seems to be lacking. Especially if you read through these forums
(hope I don't get burned for that, haha)
Depends on your flavor of unix, but:
1. Building a host.
2. Hardening a host (there's that security thing again).
3. Mirroring (including recovery from a failure).
4. Fixing sendmail the right way.
5. Maybe a bit on DNS (again, depends on your deployment)
6. Whatever name service you're using.
7. You didn't mention any network stuff. So plumbing an interface, ping, routing, snoop, debuging ssh.
8. If they support users? Maybe print stuff, setting up filters, enabling printers, canceling/moving jobs...
9. Backup environment.
10. Logging, what gets logged where and how to increase it.
11. Performance tools (iostat, vmstat, sar, prstat, etc...).
12. Misc investigative tools, pfiles, lsof, ipcs...