The colloquial British-English phrase to pop one’s clogs means to die—synonym: to kick the bucket.

In this phrase, the noun clog ¹ designates a shoe with a thick wooden sole, but the acceptation of the verb to pop is obscure. If this acceptation is to pawn, the phrase may be explained as pawning one’s clogs before death, when there is no further need for them—although this explanation sounds far-fetched. It has also been conjectured that the phrase is an elaboration of to pop off, meaning to die.

¹ Clogs were the workers’ traditional footwear in the British manufacturing districts—cf. meaning and origin of the phrase ‘like one o’clock’.

These are the earliest occurrences of the phrase to pop one’s clogs that I have found, in chronological order:

1-: From Hawporths O’ Yorksher, published in the Shipley Times and Express: Mid-Week Supplement (Shipley, Yorkshire, England) of Wednesday 13^th May 1914:

A Joakin’ Parson.
A parson whoa preyched t’ anniversary sarmons at t’ Idle ² Baptist Chapil capped t’ congregation wi’ t’ annanncement, summat like this: “T’ choir ’ll nah sing; be nut afraid.” T’ fowk wondered what they hedn’t ta be flaid on, but they “tumbled” when t’ choir strewk up t’ anthem “Be not afraid.” T’ same parson said ’at it wor noa ewse botherin’ abaht pilin’ brass up, ’coss noab’dy could tak’ it wi’ ’em when they popped ther clogs; in fact, he said, it ’ud melt afoar they gat ta t’ other side. He must think rich fowk ’ll hev a wahrm passage as weel as a wahrm reception!
     in standard English:
A Joking Parson.
A parson who preached the anniversary sermons at the Idle ² Baptist Chapel capped the congregation with the announcement, something like this: “The choir will now sing; be not afraid.” The folk wondered what they hadn’t to be afraid of, but they “tumbled” when the choir struck up the anthem “Be not afraid.” The same parson said that it was no use bothering about piling brass up, because nobody could take it with them when they popped their clogs; in fact, he said, it would melt before they got to the other side. He must think rich folk will have a warm passage as well as a warm reception!

² Idle is a suburb of Bradford, in Yorkshire.

2-: From “Talk Lancashire or Belt Up”, the BBC language handbook—as quoted by Miles Kington in All You Need to Know About the North, published in Pick of Punch (London: Punch Publications Limited in association with Hutchinson & Co (Publishers) Limited, 1970):

He just popped his clogs.
“I hope he takes his socks off more quietly.”

[The Oxford English Dictionary (3^rd edition, 2006) made an error when quoting Pick of Punch—cf. footnote.]

3-: From the column Just a moment, by Peter Fairley, published in the Evening Chronicle (Newcastle-upon-Tyne, Northumberland, England) of Thursday 23^rd November 1972:

Talking about Greek tragedy—and who isn’t these days?—what I know of the subject could be engraved on Mrs. Jacqueline Onassis’s ³ smallest diamond and still leave room for the football results.
However, I do know about a chap called Aeschylus, a man of morbid disposition, who wrote around 72 plays of woe before signing off for the last time in 456 B.C.
Only seven complete works of his are still knocking about and, as far as your man can gather they are no threat to Coronation Street ⁴ in the popularity ratings. The fashion of his death, however, deserves a better fate.
Aeschylus, who earned his crust by the most doleful of scribblings, popped his clogs in the most untragic manner possible to conceive outside Meaty Python’s Flying Circus ⁵.
He was, believe it or not, strolling around Greece one day, doubtless musing on how many corpses to strew in his next play, when there happened above him an eagle.
This fowl was carrying in its beak a tortoise which it had earmarked for its dinner. The poser facing the eagle was that tortoises come gift-wrapped in hard shells. But being an educated bird, the eagle knew how to crack that problem.
What was needed, the eagle decided, was a hard stone. Now, as it happened, old Aeschylus was balder than a shaved egg and, from above, his shining pate looked for all the world like a chunk of rock.
Mr. Eagle released the tortoise which descended at a fast rate of knots before colliding with the playwright’s skull, causing a blinding headache followed closely by a severe case of death.

³ In 1953, Jacqueline Lee Bouvier (1929-1994) married John Fitzgerald Kennedy (1917-1963), 35^th President of the USA from 1961 to 1963. She married the Greek shipping magnate Aristotle Socrates Onassis (1906-1975) in 1968.
⁴ Coronation Street is a television soap opera created in 1960, set in Weatherfield, a fictional town based on Salford, near Manchester, in north-western England—cf. a Lancashire phrase: ‘the full monty’ and meaning and origin of the British phrase ‘big girl’s blouse’.
⁵ Monty Python’s Flying Circus (1969-1974) was a sketch-comedy television series created by, and starring, the British comedy troupe Monty Python—cf. meaning and origin of the phrase ‘a nod is as good as a wink’ and meaning and origin of the phrase ‘nudge, nudge’.

4-: From the column Keith Waterhouse ⁶ on Thursday, published in the Daily Mirror (London, England) of Thursday 13^th June 1974:

The middle classes, quite rightly, like to think of themselves as a dynasty […]. Let’s look at them in that light, then, and see what kind of picture emerges.
We’ll take a moderately well-off middle class couple who were born, shall we say, in 1920 and who, according to the actuarial tables, are due to pop their clogs around 1990. They would have married in the mid-nineteen-forties and produced perhaps three children. These three would have grown up and in turn married and hatched another three children apiece. And so the line continues.

⁶ Keith Waterhouse (1929-2009) was a British author and newspaper columnist; he coined the term red masthead—cf. origin of the British journalistic term ‘red top’.

5-: From Malcolm Grey reviews the holiday films, published in the Evening Chronicle (Newcastle-upon-Tyne, Northumberland, England) of Wednesday 24^th December 1975:

Starting on Boxing Day, “Mr Quilp” ⁷ (U, ABC-2) stars Anthony Newley and, while no “Oliver,” is by no means as bad as it sounds.
In fact, for a film lasting nearly two hours, it remains throughout, surprisingly entertaining.
Newley, as the joke villian [sic], Quilp, sings songs which have genuinely witty lines. The other musical items are pleasing without being memorable.
As the title indicates, the mealy-mouthed hunchbacked fixer hogs the show, leaving little share of the limelight for Little Nell.
One disadvantage for the musical format is the absence of a happy ending. There will be few who do not know that Nell is going to “pop” her clogs, although it must be admitted that, as played by 12-year-old Sarah Jane Varley, this Nell croaks well.

⁷ Based on The Old Curiosity Shop (1841), by English novelist Charles Dickens (1812-1870), Mister Quilp (1975) is a British musical film directed by Michael Tuchner, starring Anthony Newley and Sarah-Jane Varley.

Note: This is how the Oxford English Dictionary (3^rd edition, 2006) quoted Pick of Punch (1970):

He was forced to retire in 1933 after a disastrous Catholic/Protestant punch-up among the bugs. He’s just popped his clogs.

But, in fact, “He was forced to retire in 1933 after a disastrous Catholic/Protestant punch-up among the bugs.” is unrelated to “He’s just popped his clogs.”. This is the relevant extract from Pick of Punch:

Bootle, where the bugs wear clogs.
A reference to the famous though long defunct Knowsley’s Bug Circus of Bootle. Sid Knowsley trained his clog-shod, chain-smoking troupe of performing bugs until they could re-enact any given dock strike, Liverpool-Everton match or Saturday night function. He was forced to retire in 1933 after a disastrous Catholic/Protestant punch-up among the bugs.
He just popped his clogs.
“I hope he takes his socks off more quietly.”