Rosario's restaurant!
Riverwalk (a must!!!), Alamo, Riverwalk Mall, Fiesta Texas, Sea World, Guadalupe River, Mercado, San Antonio Zoo, IMAX theater, Botanical Gardens, shopping in San Marcos (amazing outlets!!!)....much more stuff to do. If it was still basketball season, you could catch a Spurs game.
If you do nothing at all, please go to the Riverwalk!