To bring home the bacon
Until modern agriculture, people had pretty simple diets. In South China it might be a bowl of rice with some vegetables and occasionally some salted fish. In Europe there was bread and soup.
A pot would be kept over the fire and vegetables dropped in as they became available. The liquid could then be served with big pieces of bread. Sometimes, as a luxury, there might be bit of salted pork (bacon) to add fat and flavour.
A pig was most people's main hope of some meat. Pigs could feed in the forest and it was a big day in autumn when the local pigs were slaughtered. Every last bit of the pig was made into something to eat and, of course, salt was used generously to keep the meat from going bad.
Bacon was naturally a symbol of doing well. Bread was the staple you could not live without (Bread is still a slang term for money); bacon was a bit better than that.
A man who could bring home the bacon was doing well. Later on, the phrase would refer to earning a decent wage and being able to buy pieces of bacon. Gradually as prosperity increased bacon became the centre of the English breakfast.
There is a tradition (that seems to live on mainly in the States) of greased pig competitions. You cover a piglet in something oily and the young men have to chase it, catch it, and, most difficult of all, hold on to it. The winner takes home the pig/bacon. Some people say the idiom arises from this but the simpler explanation is preferred.