If you have the chance to try Kletzennudeln you should definitely do it. They are an exceptional Carinthian specialty you can very rarely get anywhere: Sweet noodles filled with dried pears and soft cheese. Be best Kletzennudeln are the hand made ones made with minced dried pears, rather than the lower quality version using pear powder.
Some salads are made with Kernöl (green pumpkin seed oil), a Styrian specialty. Even though it looks frighteningly (dark green or dark red, depending on lightning conditions) it has an interesting nutty taste. A bottle of good, pure Styrian Kernöl is very expensive (around 10-20 Euros), but maybe one of the most Austrian things to take home. (Beware of cheap Kernöl, sometimes sold as "Salatöl". Be sure to seal the bottle appropriately, the oil expands when slightly heated and leaves non removable stains. Just in case, sun light occasionally removes them, though.) Kernöl or pumpkin seed oil is also available in some online shops.
Manner Schnitten are a very Viennese sweet specialty, but just the square form factor and pink packaging are really unique. You can buy them everywhere. (Maybe you've already seen these as a product placement in some Hollywood movies or for example in "Friends" and wondered what they are.)
Powidl is a type of savoury prune jam with alcohol, another speciality from Vienna. It makes a good present as it tastes exotic and is hard to find anywhere else in the world.
Sachertorte is chocolate torte with chocolate icing and filled with apricot jam. It should be be served fresh with freshly beaten, lightly sweetened cream, which the Austrians call "Schlagobers". The original is available in Vienna in the Cafe Sacher, but similar cakes are very common in many other vienese Cafes.