Thank you, Selena.
I would like to note that I, too, have backup music; ironically, it is in a digital form (though still different: I use MiniDisc technology to download the few songs that I need, which are not available on vinyl, and to record songs from vinyl, just in case). With two music libraries and two sound systems at the event, I can provide a written, full-compensation guarantee that states that there will be no loss of music because of any fault of mine or my equipment.
I would also like everyone to note that, even if a DJ has an AVLA license, as I do, the DJ is still not permitted to download songs from the internet unless it is from the AVLA's site. And, even if a DJ has an AVLA license, it is also illegal to give "promotional" CD's of copied music; if it were legal, then I would also provide this popular feature. You can read all of the necessary information yourself, at:
http://www.avla.ca