An uncommon card that increased the amount of cargo a ship could carry would be nice, by about 30. It would target a specific ship.
It wouldn't make a huge difference to profits in the short term, but over a long period it would subtly earn the player a lot. It'd be especially helpful to newer players with just one or two ships if they're lucky enough to get it.
Again... I'm abysmal with names for this sort of thing XD