I have never seen so much fruit and grocery for such low prices. Two kilo of grapes for 1 euro. 3 kilo of prunes for 1 euro's.
Clothes, shoes. Fish inside the Mercato building. I am sure the mercato is on friday morning and saturday. Perhaps also on other days ? You can combine it with a visit to the Duomo (watch out....the Duomo is closed between 12.30 and 15.00 hrs).
The market place in Piazza Repubblica, also known as Porta Palazzo, is the best multi-cultural market I know about in Northern Italy. Only in the morning, or up to 4 pm on Saturdays.
The picture shows Walter, my favourite plant supplier: he's very dedicate, but he has not a permanent stall in Porta Palazzo market place, just in piazza Nizza.
Each Saturday is the Balôn, a large flea market near the city's marvelous cast-iron-and-glass food markets; on the second Sunday of every month an expanded version, the Gran Balôn, draws dealers and customers from all over the region.