Irakisch kass
The long row of Middle Eastern produce vendors in Brunnenmarkt terminates at an excellent food cart: Irakisch Kass. Tasty beef shawarma and veggie-packed falafel sandwiches can be had at friendly price points. You could combine a visit not only with the market, but with the outdoor bars along the neighboring Yppenplatz, the hangout of Viennese alternative types who've been priced out of the city center or turn up their noses at downtown's bourgeoisie.
To remain unbiased, I visit all places incognito and pay for my own meals and drinks. I rely in large part on readers to support my work. I'm grateful if you consider making a one-time payment (PayPal, Venmo).