São Paulo has a subtropical climate with warm summers and mild winters, while Ilhabela has a tropical climate with warm temperatures year-round. It's a good idea to pack light, breathable clothing for warm temperatures, as well as comfortable walking shoes and sunscreen. For Ilhabela, be sure to also pack swimwear and beach towels. In both locations, a light rain jacket or umbrella may come in handy during rainy periods.
Portuguese is the official language of Brazil, although many people in São Paulo speak English. On Ilhabela, English may be less commonly spoken, so it's helpful to learn some basic Portuguese phrases before your trip.