If you had one of those Gps thingeys, you could just call up POI/Grocery store, barring that, the airport is close to leaving town, not much out there - in terms of grocery story.
You want a Smiths or Albertsons probably, If it were me I would probably head East (backtrack) on I-80 about 2 0r 3 miles to 215 south. Head south, looking for a shopping mall type area. That way when you are done it's an easy trip back onto I-80 west - staying out of Salt Lake traffic.
You could also find a grocery store in Tooele - about 20 miles west on I-80 - but the town is a ways off the freeway.
Carl