Here a few tips for you if you're new to the University of Vienna and want to find someplace to eat near the University (apart from McDonalds).
Coffeeshop Company: right at the Station Lange Gasse opposite the AAKH Campus. Good Coffee and Snacks and not too expensive, although most of the time quite crowded.
Café Merkur: only 5 minutes from Campus by foot (adress is Lammgasse 1). Okay food for a low price, but the service can take a while, so you shouldn't be in a hurry.
Kaffeeküche: right at the Tube/Tram Station Schottentor. Very small, so almost no space to sit, but serves the best coffee in the area. Also check out the snacks! Perfect for the coffee you need in the morning before going to class.
Café Maximillian: opposite the Votiv-Park between Main University and AAKH Campus. Don't fall for that - you pay too much for bad coffee and the waiters can sometimes be quite rude.
Weltcafé: Situated in Schwarzspanierstraße 15 outside Campus. Relies on Fairtrade products and offers also a big variety on vegetarian and vegan dishes. Try their all day breakfasts for just 5,90€ (coffee/tea included!) or come on the weekend for the brunch buffet (13,70€). Great for group work.
Coffee Pirates: Just when you go out of Court 5 and cross the street at Spitalgasse 17. The produce their own brand of coffee and offer free WiFi when you sit down to study. Apparently the serve "the best chai latte in Vienna" (quoted from an EcoS student) and have really good pitas to eat as well (recommendation from a Japanese Studies Master student).
People on Caffeine: Across the street from the main entrance to the campus at Alser Straße situated in a part of the church (Schlösselgasse 21) you will find this very small, but personal coffee shop. They offer filtered coffee, a variety of espresso coffees and teas for take away or stay. Pastries are delivered from a small pop-up bakery in the 18th district (12 munchies) and are simply delicious. The owner is really friendly and will definitely have a chat with you. Nice for study breaks.
Unibräu: right on Campus in Hof 1. Austrian quisine to a reasonable price, quick waiters and meeting place for EcoS-Roundtables.
Stiegl Ambulanz: also right on Campus in Hof 1, opposite Billa Supermarket. Good food, but expensive.
Ie Ga: opposite Campus in Lange Gasse. Very good Korean Restaurant, but unfortunately not too cheap.
The Pie Factory: opposite Campus in Lange Gasse. Small shop with sweet and spicy pies, which make a great snack between lectures.
Mensa of the Afro-Asian Institute: A little walk from the campus just next to the Votiv Church (Türkenstraße 3) this student mensa is usually quite crowded. Only because it is so good! Three different main meals (one vegetarian) each day for lunch time with soup, salad and/or dessert. Make sure you get a "mensa sticker" from the ÖH-office on the campus (court 2, next to C1) to get a 50cent discount on the 5,70€ full meal.