Walk up Marquette Avenue for your lunches. You'll see a bunch of food trucks. My favorites right now on that stretch are Vellee Deli, Get Sauced, and Hola Arepa but it's hard to go wrong with any of them.
If you walk up 2nd Avenue from the Convention Center, you'll see the awning for Ruth's Chris Steakhouse at the corner of 10th St. Enter that building, go up the escalator right in front of you and look to your right -- you'll see Cafe Patteen which has outstanding coffee and breakfast baked goods (scones, varying muffins/rolls depending on the day, cookies). This would make a quick and convenient start/cheap breakfast only 2-3 blocks from the Convention Center.
Porter & Frye in the Hotel Ivy (1 block north of Convention Center, also on 2nd) has some good lunch and happy hour deals. They have a small patio to enjoy today's beautiful weather.
Hell's Kitchen is my favorite breakfast place in the US, bar none. Always go there whenever I am in Minneapolis, as I am now. Had the Lemon Ricotta Pancakes today and am debating whether to get my old favorite, Mahnomin Porridge with a side of Buffalo Sausage toast (topped with the housemade peanut butter, of course) or the cornmeal pancakes the table next to me was raving about, when I go back there tomorrow.
Oh, decisions, decisions.
By the way, they have some pretty interesting sandwiches there for lunch, too.