p.p.s. I remember when I first heard 'Boxing Day' as a child. I couldn't understand why folks would be 'duking it out' on the day after Christmas!
Clearly you've not been round our family for Christmas... post overthrown Monopoly game... ;-)
Some Traveller world festivities:
The Coming of the Winds - the day of year in which a regular southerly wind starts up bringing warmth/rain/whatever
Fifth Night - a celebration during Jump for passengers to let their hair down and perform party pieces
Jump Day - a remembrance of the invention of Jump drive giving the race the stars
President's Day - the day they strung up the incumbent and replaced her with a charismatic dictator
Quarter Day - on a rockball with enclosed habitats and not a lot to mark the seasons just divides the calendar into four; some ancient customs involve the giving of a low value coin to loved ones