Snorkel equipment reservations are under Port Adventures, so if you do not cancel 3 days out, you may be charged. That being said there are plenty of bikes, floats, snorkel equipment, etc., so no need to book ahead for any of those.You don't pay for it until it happens, so I would just pre-book it. I imagine if it was a bundle, they would just prorate what was charged to the stateroom.