That's so great man I'm so happy for you. Austin is a fucking blast!
Don't waste anymore time, get right to North by Northwest (restaurant). It's not your traditional Texmex, it's what I'd consider Texas New England comfort food. I'm not shitting you, it is the best food I have ever had. Ever. Burgers, pastas, we ate there at least once a day when I was down there. And it's a brewery and their brews go so superbly well with their food it's fucking ridiculous. Go there, post pics of what you get, and I'll PayPal the cost of your meal to you as a congratulations on your freedom and a send off for school. No joke, I mean it.
6th street is where it all happens, so much going on. So much live music. It's an overload.
There's a fucking village of food trucks.
Bat bridge is a gay touristy thing but what the hell see it too.
Fucking gorgeous women everywhere you look.
Look around and take it all in. The sights you're seeing is what a booming economy looks like. Austin is basically two cities, the existing city and the city of sky cranes, the city being built.
Spend some time driving around hill country. Most beautiful piece of the country I never even imagined existed. It's what I always pictured the Hollywood hills looks like, but in the middle of the desert. It's just reeks of success.
There's a cool little military museum too but I don't remember the name.
There's no reason to venture south to San Antonio. Maybe just once, go see the Alamo and the Riverwalk, and otherwise just go see how fucking expansively sprawling it is. It's bigger than anything I've ever imagined. If you can get to a vantage point of high ground to look around, you'd think the city itself is the size of CT. You can't tell where the city ends and the nothingness begins. And I mean nothingness. There's two hours of nothing around it in every direction, it's wild. But it's what I always imagined the bad parts of Mexico to look like. Ha!
Good luck man, have fun, enjoy it, study hard. Take me up on that meal, too. The place will become a staple for you.