The Houston Zoo is amazing. I would highly recommend walking around and seeing the animals.
If you are looking for a baseball game. Look no further, the Astros play 9/1-9/6. Click the link to browse your ticket options.
If you go to aquariums in every city you visit, the Houston downtown aquarium is a must-stop spot.
If you like to shop, the Galleria is a bustling mall with every shop one could imagine.