That would be the operating system disks. Most likely the operating system is already installed, but knowing which one would be useful.The one I'm using now is OSX 10.4.11.
Apple call it some kind of big cat- Jaguar possibly. The latest OS is 10.5.1, and that is called Leopard, and there are still some issues with the way that works with some music programs. Lepoard will only work on Intel Macs- not the old ones with Power PC processors from about three years ago.
So you need to know:-
Is it an intel processor?
What version of OSX does it have?
You can find the answers to these two questions if you click the little Apple at the top left of the screen then select "About This Mac"
Finally the big question.
Will they reinstall it for free if anything horrible happens (like a hard drive failure- out of twenty students with Macs, I've seen two of these this year)
And always remember, Macs never crash.
Mac devotees will believe that even after staring at the whirly beachball of death for a week!
Cheers
Dave