I believe Nitrox and drysuit are the 2 specialities you'd be required to have if you want to dive nitrox or rent a drysuit. So eventually, they'd become a must have.
Basic wreck is also the one most agency would require to go to the next level.
Beyond these 3, all others seem to be a matter of choices and preferences.
Basic wreck is also the one most agency would require to go to the next level.
Beyond these 3, all others seem to be a matter of choices and preferences.