Gruel is basically thin oatmeal, and the meal is not bad at all. Even if it's nothing compared to the decadence of First Class, it was probably the best food many of the poor immigrants ate in their entire lives- and was leagues better then contemporary competition, which expected migrants to bring their own food (!!!) for the journey.
Also, the dude who baked all the bread on that menu (Charles Joughin) not only escaped and survived the frigid water, he saved a whole bunch of passengers, too. While allegedly quite drunk