Ooh, good topic.
Wind is a big one, but I’ll go with resources/resource management. Most of my favorite strategy games are about managing resources in some way. Gold isn’t really a resource since you can’t exchange it for anything except in the case of Carbon Charlie and some random RotF ship. It seems like it would’ve had to have been something in the game from the start, as suddenly adding a new universal game mechanic is not something Pirates CSG ever did.