The San Antonio Taco Company is the restaurant that sits next to every university -- the cheap taco/burrito place that's always hopping. SATCO, as it's known, is a reliable place to hit when you've only got $5 but don't want McDonald's.
You get what you pay for in terms of do-it-yourself service: you have to stand in a (usually) long line, fill out your own order slip, get your own drink and salsa. But there's a great outdoor deck with lots of tables where you can relax with friends; no one rushes you off even though you only spent a few dollars.
SATCO is in a great location, across from Vanderbilt on 21st Avenue South; those cheap tacos leave you a few dollars that you can spend on ice cream at the next door Ben & Jerry's or coffee at Starbuck's, just down the street.