Pie In The Sky

"Pie in the sky" comes from a song that was written by the Industrial Workers of the World (AKA the WW or Wobblies). They were an early American union.

In 1911, they used a rallying song with the line "Work and pray, live on hay, you'll get pie in the sky when you die."

The idiom came to mean an empty wish or promise since no one would really want "pie in the sky" but would want something here on Earth.