I'm from São Paulo.
Well,AFAIK.the Ipiranga Museum is the largest historic museum we have at São Paulo (the state).Unfortunately,there's nothing about brazilian expedition at WWII.But there's a room with a couple of weapons,some used at the Paraguay War and others from the 19th century.But it's a place I recommend for tourists.
The Mercadão (Central Market) is a place you definitely should have a look.It haves good places to eat inside it.Also,there are stuff there that is hard to find outside the northern,northeastern and central regions of Brazil.
Like Rommel said,açaí is the word.
The Ibirapuera's Park is the largest park in the city.It's a hotspot for younger people,bikers,skaters,joggers,people that like playing football or like doing some more "unorthodox" things,like slacklining.The most curious part of the park is its RC hobby area.There's a tank for RC ships,a round track for those RC planes that are tied to a rope and nearby there's also a warehouse with a large RC train set and IIRC a slotcar track as well.
IDK if you might be interested,but we have the largest japantown in the world,Liberdade neighborhood.
Anyway,if you're coming to São Paulo and you need help,you can ask me.
