Saturday: nice flee market on the Plaine de Plainpalais (tram 15 from the train station, 10 minutes to Plainpalais stop), until 6 pm.
Saturday: small food market in Carouge, itself a cute neighborhood (tram 12, get off at Marché ), until 2 pm.
Sunday: big food market on the Plaine de Plainpalais (tram 15 from the train station, 10 minutes to Plainpalais stop), until 6 pm.
Anytime: drinks or food at the Bains des Paquis, relaxed spot on the lake (10 minute walk from the train station)
Enjoy!