(I'll try to keep this short as
it is a writeup concerned with Dwarfs)
The dwarf-bread of Discworld was created by Pterry to parody the elf-bread, or lembas, of Tolkien's Middle-Earth. Like all things Elvish, their waybread was perfect: Tasteful, nourishing, and durable. Well, the bread forged by the Dwarfs would also last long to a traveller - in fact, he would put off eating it for as long as dwarfly possible, and then think about it some more.
The Dwarfs regarded their bread with great pride, even worship. The legendary Scone of Stone is an artefact of great ceremonial importance and a major part of the plot in The Fifth Elephant. The bread is a symbol of the hardness of dwarfs - no cutlery can break it! - but unlike other symbols, it also acts as a versatile weapon when needed.
The Scone of Stone also parodies the solemn, slightly ridiculous significance of the Stone of Scone in British tradition. This Stone of Destiny was used to crown every Scottish king before the English got their hands on it, and is now an importan symbol during the coronation of the ruler of Britain.
In a similar way, every new Dwarfish Lord of the Mountain is required to sit upon the Scone of Stone when assuming his responsibility. In either case, nobody can say why, and yet, the stone, or the scone-stone, is of great importance.
The antonym to dwarf bread is spaghetti.