I technically work in the Kluczynski Building but I'm hardly there anymore.
Chicken Planet (a bit of a walk to Wells / Van Buren) is decent and incredibly cheap, provided you like grilled chicken.
Oasis Cafe (21 N Wabash) is always a good place to hit for Middle Eastern.
Halo Asian Mix (29 E Adams) has Hawaiian, Filipino, Chinese, and Japanese (I've only tried offerings from the first two categories).
If you want to stuff yourself with sole, get a fried fish "sandwich" (more like a pound of lightly-battered sole on a plate with a sesame seed bun thrown on for garnish) at Cellar's Market in the basement of the CBOT (Lasalle / Jackson). They also have a decent chicken pot pie on Thursdays.
A little bit of a hike, but the new Ba Le spot (166 W Washington) has pretty good banh mi. Better than Banh Mi Express (105 W Madison) which is hidden in a soulless basement food court.
And because it's nearby, I'll mention Cavanaugh's in the Monandock. Meh.