In my experience, never ever make internet access essential to any presentation. Ideally, the complete presentation is self-contained and doesn't need anything beyond the presentation program to be installed in the default manner. Relying on an internet connection or an (unknown) Perl installation is just asking for trouble if you can't test it beforehand.

In the past, when overhead projectors were available, I would also make overhead slides. My basic rule of thumb is to assume that anything under your control may fail and anything not under your control will fail. Ensure that you have fallbacks almost up to the rediculous. Only you can decide what the rediculous is :)