Regina's pizza on the corner of Union/Utopia is decent, as well as Double J Deli further down on Union, across from 7-11. To be honest there's not much of a "you have to go there" type place in the immediate area, but a lot of the options around are solid, reliable, good food depending on what you want.Would you recommend any in particular that you like or have been to?
I forgot that classes are in session (vs. the Open Cup during summer when everything on campus was closed), so the D-Angelo Center on campus has a Starbucks upstairs as well as a food court downstairs. That may be your best bet for variety of food and also being close to the field.