The cafeteria at Tresidder Union, and the Coffee House, are about the best places on campus to find complete meals for breakfast/lunch/dinner, and coffee.
This is in the basement of Jordan Hall, Building 420 (that's next door to the Linguistics Dept). They have a rotating Thai menu 5 days a week, plus various noodle salads. The line is phenomenally long between 12 to 1pm, but it moves at an acceptable pace.
In the basement of the Political Science building (160; go round the back at ground level, and head down the steps). They have snacks, sandwiches, and weak coffee.
Other eateries to check out: The Bookstore Cafe (on the 2nd floor), Medical Center Cafeteria, Business School Cafeteria (they have a similar menu as the Tresidder Cafeteria, and are noisier), the Cubberley Cafe, the Law School lounge, the SEL Eatery (in ERL) and the Terman Engineering Lounge (Nuts 'n' Mud).