I am alway preaching about the need for a backup plan when you are making a presentation. Have a spare bulb for your projector, or even better, have a second projector on standby. Have spare batteries for your remote. Have a copy of your presentation on a flash drive in case your computer fails.
But here is another idea. You can now have a fully functional backup copy of your presentation on your iPhone. Apple has released a version of their popular Keynote presentation software for the iPhone. If you have already created your presentation in Keynote, you are good to go. If you are not a Mac user, or prefer PowerPoint, no problem, Keynote can easily import a PowerPoint presentation. So here is your backup plan. Buy a copy of Keynote for your iPhone ($9.99 in the App Store), pick up an an Apple VGA adaptor ($35.00 at the Apple Store), and you are good to go. If your computer fails, you can hook up your iPhone, and you have your complete presentation, ready to go.
Just a few things to be careful of. The iPhone has a smaller selection of fonts than your computer, so run through your presentation on the phone to make sure it hasn’t made any weird font substitutions. Some of the fancier animations and slide transitions that work on your computer might not work on the phone.
You will need a recent iPhone for this to work, the older phones don’t have the processor speed to run Keynote. If you aren’t an iPhone user, you can pick up an iPod touch for $199, still cheaper and a lot lighter than a spare computer. And you can always use the iPod as a remote (see HERE) to control the presentation on your computer or iPad.