There is luggage storage (at least 5 yrs ago) which I have used, called Malex. Fairly pricey. As you come out of int'l arrivals they're outside the terminal, to your right (near the taxi rank). The link below gives you the phone numbers, would be worth finding out what time they'd open...

http://br.answers.yahoo.com/question...5023919AA89YFZ

Getting into town and back, it could almost be worth renting a car with GPS, as a bus will set you back R$20 each way, from where you'll probably need to take taxis, which arennt cheap in SP etc. But then there's the cost of parking...

Places to visit are the MASP, Ibirapuera Park, maybe some nice sushi at the rooftop of Cidade Jardim mall, and perhaps a breakfast taking in the view from the rooftop terrace at the Unique Hotel.

Make sure you factor in a good 2hrs on the way back. No need to be at check in any earlier than T-90.