Contract Bridge (game)
For other uses of 'Contract Bridge' see Here
Contract Bridge is a fiendishly complex game of cards played by two teams of two, each of whom occupies a notional point of the compass. Each player is expected, without directly communicating, to be able to deduce which cards are held by the other three players, and respond accordingly. (ie, to support their team-mate and block the opposition)
A four-handed game of cards is therefore ideal for Death, War, Famine and Pestilence as a way of filling in time before the outbreak of Apocralypse.
The standard primer on the Disc is Nosehinger on the Laws of Contract. There is very definitely a copy in Death's Domain, as Twoflower used his copy as a teaching aid when explaining to the Four Dread Riders how the game was played: when he and Rincewind left in something of a hurry, they left the book behind.
It adds an extra dimension if played with Caroc Cards.
Now Ronnie Soak has apparently re-joined the group in his role of Kaos after a successful gig against the Auditors, the search must be on for an equally absorbing five-handed card game...
In The Last Continent, the Chair of Indefinite Studies suggests bridge would be a good replacement for sex as a method to propagate the species. When someone points out that bridge requires four people, he suggests croquet as an alternative.