I love words and idioms, so I’m going to geek out here.
cold turkey: fairly recent, goes back to the early 1900s. Might be a derivation of “to talk turkey” or from the dish cold turkey, which would need little preparation.
chewing the fat: goes back to the 1400s when they “chewed the cud”. Can also be replaced with “rag”. Basically refers to working the jaws in complaint, gossip, or idle speech.
Source: 2107 Curious Word Origins, Sayings, and Expressions by Charles Earle Funk
Bob’s your uncle: Bob’s your uncle’ is often said to derive from the supposed nepotism of Lord Salisbury, who appointed a favourite nephew, Arthur Balfour, to several political posts in the 1880s. Balfour went on to become Prime Minister after his uncle, but his early political appointments were considered inappropriate as he had shown no prior interest in public work. It is unlikely that Arthur Balfour would ever have become a celebrated politician without the patronage of his influential uncle. Piers Brendon, in Eminent Edwardians, 1979, writes:
"In 1887, Balfour was unexpectedly promoted to the vital front line post of Chief Secretary for Ireland by his uncle Robert, Lord Salisbury."
The link here between an uncle Bob who was Prime Minister and a ‘Bob’s your uncle’ passport to a cushy life is easy to make.The fact that the word ‘nepotism’ derives from ‘nephew’ makes the link seem all the more neat. Such neatness is often the mark of a back-formation, that is, an explanation that is made up after the event.
Just as an aside, a variant of the phrase has been taken up by the Greek community in Australia. They use ‘Spiro is your uncle’ to denote nepotism there.
Source: http://www.phrases.org.uk/meanings/bobs-your-uncle.html