Remember that this is training on how to use life support systems and what do if something goes wrong.
On the one hand, all you really are doing is breathing underwater and you are spending the time getting familiar with the gear and how to use it. On the other hand you are breathing compressed gas (air) at depth and there are some very serious issues when doing so to keep in mind or you can die!!!
One of the most knowledgable, experienced dive instructors here in LA used to say I can teach you to dive in one quick sentence: ALWAYS BREATH! The rest is technique.
While this statement is a bit flippant, it's also very accurate. Its when you stop breathing or hold your breath that problems develope.
When choosing gear, comfort and fit are the two most important components. The more comfortable you are in your gear and at depth, the better off you'll be, both in your enjoyment and your safety. If you have an average height & sized body, then most rental places will have gear for you. If you are heavy, tall, small or otherwise a bit non-average, having your own gear can make things more enjoyable. Fins, mask, snorkel & booties (where apropriate) are good things to own. I priced these at the local dive shop the other day and nearly fainted at what some of these cost.
I'd also recommend you do as much of your course work from home, including water work if possible so you can spend your time on your vacation enjoying the sights and experience. If that's not possible, try what Icarus recommended and do your book work at home and your water work on your trip.
I've been a certified diver for more than 27 years and in the water with fins, mask and snorkel for nearly 40. There's no substitute for experience.