If you push the boat out it means you spend more money than you normally do, especially for a celebration.

Examples:

Rob's wedding was amazing; they really pushed the boat out and made it a day to remember.

As it's our anniversary, let's push the boat out and buy a bottle of champagne!

Take note

If you miss the boat, you miss a good opportunity because you wait too long.

Example:

Sorry John, the deadline for applying for the job has passed. You've missed the boat.