These are some substantially successful local vendors:

1) Bigalora has a huge following for thin-crust pizza. The one in Ann Arbor is excellent.
2) The Plum Market/Zingerman's will provide you with grab-n-go gourmet ($$$) options. Plum Market is a locally-owned boutique whole foods. Superlative food quality.
3) Andiamo is popular but "meh" Italian. Their flagship is in GM world headquarters in downtown Detroit.

These are all net gains for DTW transit passengers. I hope you enjoy these as much as the locals do.