Whether you call it pétanque or boules, the traditional French game with the shiny silvery balls has made a comeback. It used to be the only people you'd see playing in were old men in berets sipping pastis. Now everyone plays, particularly Parisian hipsters (les BoBo's) who don't have to worry about breaking a sweat.
In the mood to try your hand? You can learn the rules of pétanque here, and find a great list of places to play here, but what about les boules? You can either buy inexpensive sets of balls at sporting goods store like Decathlon or from pro shops like Obut. You'll probably see another game with little wooden pins, almost like bowling. That Jeu de Quilles, a Finnish game that has become more popular around Paris, possibly because the equipment is lighter and less expensive, and little kids can play. Not sure where they rate on the cool-o-meter, though. Stick with boules unless you're devoid of hipster aspirations or immune to subtle Parisian mocking.
Casual pétanque games in the Arènes de Lutèce, for all ages (click here to see a cheeky angle to this pic).
If you're just passing through and don't need the extra kilos in your suitcase you can also rent them from Paris Ma Belle for just €10/person for the day, and they even deliver and pick-up the balls when you're done. Another option if you don't want to have to do anything yourself is to hire Paris Localers to take a Pétanque Tour including an apéritif and a match on the Place Dauphine.
Note that many people say you can play in the dedicated pétanque courts in Luxembourg Gardens, but they are usually reserved (and obsessively raked like a zen garden) for the local pétanque club. So feel free to play elsewhere in the park, there is plenty of space, but don't play in the reserved areas unless you get permission.
Serious pétanque player in the immaculate Jardin du Luxembourg.