I had just an overnight trip to enjoy Austin (downtown on foot), and dinner was already accounted for (UT threw a reception for the event I was attending). I had lunch at Hut's Hamburgers (870 W. 6th St.), a safety choice that already came recommended by Jane and Michael Stern, among others. It lived up to expectations; I enjoyed a Richie Valens Burger (a fine tribute to the singer: jalapenos, mayo, lttuce, tomatoes and guacamole) and onion rings, and an iced tea (not sweetened) the size of an aquifier.
Breakfast the next morning I lucked into a 24-hour place, Kerbey Lane Cafe (2606 Guadalupe, which rhymes with "quadrupe"), with no prior recommendations. It looked like a typical coffee shop, but served up a mighty fine plate of migas, with spicy black beans and a strong freshly-brewed cup of coffee. If I had such a place convenient to me in Chicago, I would hit it fairly often.
Service at both places was very friendly.