For breakfast and merienda, go to Confiteria Boston, for the best medialunas in town. There are many branches in town, one in the shopping mall, other in Playa Varese and another at Buenos Aires street.
There is a pedestrian street, San Martin, I think you are not going to find nothing special there. The two streets to go for a walk are Alem and Guemes, they are like 8 blocks away to each other.
Avenida Juan B Justo is where the wool sweters and winter jackets are sold, the traditional idea is that the are cheap, but I dont know know. At Juan B Justo near the water there is a huge market with a lot of shops, cheap in theory.
I know that many years ago you were able to ride horses at Parque Camet, further north of the city.
Surfers go to Waikiki beach. That beach has a huge restaurant buildt in eight faces. This beach if at the south, 30 blocks after the puerto. You have a wonderful sight of the city and big waves at the ocean sea.
There is a golf place near the puerto.
Santa Clara del Mar is very nice, a little town with more forest. It is 18 km north of MDP.
I ate delicious paella for many years at La Paella restaurant, located at Entre Rios street, near Moreno and Belgrano streets.
Do you speak Spanish?