As colaholics, we naturally purchase the Cola Card (flat rate for all you can drink for the duration of the cruise.) But on Oceania, where they do not offer this deal, we each openly carried a case of 24 aboard and, other than a few snickers from the staff, nothing was said.
We wonder at times just how old are those tins of cola found in the staterooms. We do not know of a soul who purchases them at that price...
Being addicted to Diet Coke (yes, I know a terrible vice) my hubby and I have a system . . . . . We pack a medium suit case inside our large suit case (pack our clothes in the medium case) and check it through on the airplane. Once into port, we take the medium case out and then fill the large case with Diet Coke and bottled water and check it through at the cruise port.
We don't take the transfers and grab a cab from the plane to the port (or hotel if we've stayed precruise for a night) and have the cabbie just stop at a convenient store along the way.
As a side note, I prefer the resealable 20oz bottles because it's easier to take them around the ship and drink as I like but I can pack a few in my beach bag and take into the ports.