Ah, parking. The problem of problems for students and faculty at every university. Parking is a bit of an issue if you are not willing to do some walking. However, Texas State is undergoing a big construction craze, with the parking issue being addressed in the form of two parking garages.
Texas State does have a decent bus service that goes around to virtually every apartment complex in San Marcos, as well as the far reaches of the campus (from one end to the other). You will find that a lot of students ride their bikes to campus, even those who do not live on campus. The buses are also equipped with bike racks, so you can carry your bike with you to campus if you don't want to bike the whole way there.