We are taking a cruise in February with our new baby, who will have just reached the required 6 month age limit. We cruised with other older daughters when they were young too, although not 6 months. We personally won't take a stroller this time, we decided on a previous trip that a good backpack carrier that stands up on its own is a better investment for us and it tends to get many less evil eyes from fellow passengers : )
We always take a small medical kit with us that includes fever and pain medication, bandaids, diarhea medication and pedialyte just in case. These things are not always readily available and if they are available, not always known by a brand name that you are familiar with or at a price that is in any way reasonable. This time we will add teething rings that we can throw in the ice bucket just to be sure that we have that option. We are travelling with a small pool for bathtime as well, I think this is the best option.
Hope this helps. I'm sure it will all be wonderful and you'll make many memories that you will cherish for a long time.