Bring lots of Purell. We just got off a Viking cruise on the Elbe River, and lots of us came down with norovirus. They don't have a hygiene protocol, like enforcing hand sanitizing before entering the dining room, just some machine dispenser that's voluntary and usually not used. Also, once the first passengers started getting sick, no one was quarantined, even those folks who were obviously still suffering but sitting in the lounge. I've sent an angry letter to Viking, but haven't heard back yet. So do yourself and your fellow passengers a favor by sanitizing frequently.

I only used my long lens once, to take pictures of some horses fighting along the riverbank. The rest of the time it rested in the room. Couldn't get far enough away from anything to need it! Used mostly wide angle, short zoom and a bright prime. There is surely no need to carry that long lens around with you, pick the most versatile wide angle you have, and don't worry with the rest. The Viking folks are gonna keep you very busy every day, and you'll be in a tightly compacted group, and also in crowds of other tourists and locals, so your photography will have to adapt. I could find no use for a tripod. A bright lens will help in the dark interiors of cathedrals and museums (if cameras are allowed anyway, they aren't allowed everywhere).

Did you feel you could have used a long lens on the ship to take pictures as you cruised along?

By the end of our cruise there was only one guy still carrying his DSLR, and his wife wasn't speaking to him because he smashed her Delft china with it on the bus.