Umbrellas, really large ones that actually protect you from the rain, can be purchased on every block in Rio and other cities for about R$10 (U$5). It is likely to be too hot everywhere you mention for a jacket. If you bring one pair of long pants, do bring very, very lightweight ones, in cotton or linen (natural fibers); jeans or even khakis would be much too heavy unless you currently live in a very hot climate where you are used to wearing them in heat/humidity.