Pop one’s clogs is a euphemism for dying or death.

To 'pop' - slang for taking something to a pawnbrokers. Clogs were used (umongst others) by poor millworkers in the North of England in the 19th/early 20th century. 'Popping your clogs' indicates the wearer was no longer in need of them, so is taken as being dead/dying (normally assumes natural death). Pawning something as important as your footwear would be the last thing you would do...

The verb to pop may be the old term for pawning goods. The implication is that someone would only want to pawn his clogs when he had no further need for them, that is, when he was about to die. But it’s also possible that it’s linked to the idiom to pop off (an abbreviation of pop off the hooks ), which can also mean to die.

Example:

Freddie Mercury's departure alone is reckoned to have put several percentage points on total British sales last Christmas. And with the recession now biting into the music industry, one desperate insider said this week: "We have a wish-list of people we hope might pop their clogs before Christmas."

Example 2: TVL's got problems, but no one says it's going to pop its clogs.