Push the boat out
To spend generously. To spend more than one is normally accustomed to doing, often to mark a special occasion.
This phrase originates with the literal meaning; that is, pushing boats from wherever they are beached and into the water. People have for centuries built boats that were too large for an individual to move. Helping a seaman to push the boat out was an act of generosity – a similar to the modern-day act to helping to push a car that is broken down.
The phrase became used in UK nautical circles to mean ‘buy a round of drinks‘ sometime during the 1930s;
“Push the boat out”, to, a boat-work term used to imply paying for a ’round of drinks’.”
More recently, ‘push the boat out’ has been used more generally and has come to mean ‘behave extravagantly, making a purchase that is rather beyond what one can afford’.