Some of the city's old-guard restaurants hold heralded places in Carnival tradition, and king cakes have been glittering extra brightly lately as chefs and bakers around New Orleans put their own stamp on its form and flavors. But, when it comes to keeping people going through the long haul of Carnival, the heavy lifting often falls to much more humble fare from unsung suppliers. These are the grocery stores, the delis and the specialty caterers of New Orleans, businesses that work at fever