I just journeyed outside the General Discussion and found this thread. I hope my input isn't too late.
For BBQ, there are tons of places. Make sure you try Rudy's in Leon Springs. It's pretty famous and pretty good. Also, if you get that way, go to Kreuz Market, in Lockhart, it's another famous BBQ place, been around since 1900.
For Mexican food, not Tex-Mex, try La Fogata. The margaritas are outstanding, but don't have more than two. Their skirt steak is good, so is their beef kebob. If you like pollo loco or enchiladas, try El Mirasol. And have a Michelada while you're there. Los Barrios is another good one - more of a "lunchy" atmosphere. They have a great chimmichurri on the table. If you like mole, it's a good place to go. If you're on the Riverwalk, consider only Casa Rio. It's been there for 50+ years. Try their queso. All other mexican places on the Riverwalk are bad. There are so many Mexican restaurants in SA that you have to wade through alot of bad, tomato-saucy meals before you stumble on a good one. Trust me, these four are good. My preference order is: LaFogata, El Mirasol, Los Barrios, Casa Rio.
For burgers, two places: Chester's and Longhorn Cafe. Fries yes, onion rings no at Chester's. Fries and onion rings are both good at Longhorn.