Langos? (my preference is savory, not sweet)
Vakvarju does a good langos. There are now a couple in town. The most convenient is generally the one on the lower end of Pauley Ede utca in district VI.
Sausage stand, crusty bread, beer? (a childhood memory)
Hús Hentesáru at Hajos utca 21 (on the side of the Opera House). Fits your bill pretty accurately. Small, to the point and always good. The last time i paid any attention they were closed on Saturday. Not sure about the beer.
Ormeny Rakott Palacsinta (Palacsinta cake)?
I’m not a diehard strudel fan. People say Első Pesti Rétesház (First Sturdle House of Pest) at Október 6 utca 22 (north half of District V) is very good. I generally just buy it at what ever baker i am walking past at the time. My favorite Cukraszda is the Auguszt Cukraszda at 14/16 Kossuth Lajos u. (South half of District V) - see the beautiful building courtyard out the back door. For the Pogacsa, eat them for free at Kadarka Wine Bar at Király utca 42.
Roof top bar with a view?
Most every bath house
Budapest Jazz Club (younger clientele) or Opus Jazz Club (higher end).
Off the grid fun thing to do?
Go drive a Russian Tank http://www.tank.hu/
under appreciated thing to see?
Empty bottle of Hungarian wine.