We pre-booked the intercity train into Rome which was amazing. It only took 40 minutes and we'd also booked tickets to the Colosseum as I'd read about the queues. What a great move as the place was mobbed. Definitely book a ticket or go on an organised tour.
You need to get the tender to Cannes which you needed to pre-book with NCL but was free. This again went smoothly annd seemed to be well organised and passed without a hitch. Cannes was lovely but best just to walk round or get on the little train which stops by the port.