Convention Center recs
Just walk up Nicollet away from downtown, as you get to the higher # cross streets, up to about 28th, the food becomes less expensive and IMO much better than anything you'll find downtown. Don't bother with Little Tiajuana (which is just a punk atmosphere- fun but not good and expensive for what it is) but anything else is at least worth a visit and you'll find just about any ethnicity you're in the mood for.
Catzen - if you're looking for a good cup of coffee and a scone-head to 2nd Ave/10th Street in the Oracle (by Ruth Chris) in the skyway - Pateen has great coffee and scones/muffins available and made fresh daily. They're killer!
If you are looking for lunch, not too far (at the corner of 9th/Marquette Avenue, not too far from CC), you will find Bombay Bistro (Indian). It's tasty, affordable and they have a quality buffet. It gets busy and you might be able to catch a sidewalk table.
820 Marquette Ave, Minneapolis, MN 55402