well carring a survival kit incase your cruise ship sinks, is a bit of a challange. I do really need spare clothing, since i certainly not planning to running around in a survival suit/wetsuit/drysuit, when on a cruise. They generally don't fit very well in a jacket pocket. Although " crazy eric " seams to do it.
Carring it as a backpack, might force you face down in the water, because of the boyancy on you back. Not sure what would happen if you wear it in front of you. I do know that jumping in the water with you PFD is bad enough. Really don't want another big thing attached to me.

Turning a PFD in a loadbearing vest for your kit, isn't to great either. Since it limits your movement and you stilll have lack of space, besides i'm not carring a PFD on a cruise all the time. So i don't think there is a perfect solution for a cruiseship...