When I need a break from conference food (not that it's bad, but it's conference food) I sneak over to http://www.mothersrestaurant.net/ for some authentic Po'Boy action that can't be beat.

My personal favourite is Famous Ferdi Special (Baked Ham, Roast Beef, Debris and Gravy) or add some cheese to make it a Ralph.  It is by far the best Po'Boy close to the convention center.  Their cup 'o gumbo is quite good too.

Café Du Monde is an obvious staple, but I prefer the atmosphere of Café Beignet in the French quarter (closer then Café du monde) next to the police station.