If you are coming through MN rather than WI, do consider a detour to see the only Frank Lloyd Wright-designed gas station, in lovely Cloquet. (
https://www.atlasobscura.com/places/fra ... as-station ).
In Duluth, Northern Waters Smokehouse every time (
https://northernwaterssmokehaus.com/ ). Duluth Grill has great breakfasts (we prefer it to Grandma's which is more famous).
The Scenic Cafe is worth the detour on the scenic drive between Duluth and Two Harbors (
http://newsceniccafe.com/ ). While you are there, you must visit Russ Kendall's Smokehouse, and you want the lake trout rather than the salmon (
http://leftatthefork.net/russ-kendalls- ... -river-mn/ ).
I prefer The Rustic Inn to Betty's for pies (
http://rusticinn.cafe/ ) - easier turnoff, friendlier service, variable but often superior (pun intended pies).
In Two Harbors, Castle Danger Brewing shouldn't be missed. Further up the shore, Grand Marais: World's Best Donuts (
http://www.worldsbestdonutsmn.com/ ) - the skizzle is the thing to get. Sven & Ole's for pizza on the cheap. We were blown away last summer by the Angry Trout but it might have been lightning in a bottle (visiting experimental international young chef people). The Crooked Spoon has been more consistent over a longer period of time there.
Zup's (Zupanich Brothers) in tiny Silver Bay is a great stockup place - seems like a sleepy grocery store but the smoked meats are on point, particularly the pepper bacon and the Canadian bacon, both which pack well.
http://zups.com/ . Here or at the Super One in Two Harbors (conveniently open late) you might run into "porketta" or "porchetta steak," which is fennel-crusted fatty pork steak / chops worth investigating. The Vanilla Bean in Two Harbors has good signature coffee; I don't recommend much else there beyond the brewery, but the spice store next door is great and if you really feel like rolling the dice try out Vietnamese Lantern with a truly unique buffet.
Wildcard: Lemon Wolf (if it's open, and they are a little eccentric). This is kitschy and nothing fancy but the fish and wild rice can be the best around, prepared simply.
http://lemonwolfcafe.com/. I'll be up there in just a few months - can taste it already.