Zehnder's or Bavarian Inn Frankenmuth for a chicken dinner if you want a big meal and have some time.
Krzysiak's House Restaurant in Bay City for Polish food and polka music if you have time.
Basement of Zehnder's for tasty German-American baked goods.
Clyde's Drive-In in St Ignace is a good stop for burgers.
Suzy's Pasty in St Ignace or Letho's Pasties outside of St Ignace along US 2. (A pasty is a dry meat pie that is associated with the UP. There are many restaurants that serve them and "the best" is a much debated topic.)
Gustafson's Smoked Fish in Moran for fresh local smoked fish and jerky (Another area of much discussion who has the best smoked fish/jerky)
Frankenmuth, MI It is a fun American tourist trap idea of how Germany was. It also has the worlds largest Christmas store Bronner's.
Alexander Henry Park Mackinaw City
Any business parking lot on the south side of US 2 in St Ignace for views of the Mackinaw Bridge.
Cut River Gorge US 2 great view of the bridge and walk down to the lake
Any roadside park along US 2 by Lake Michigan.
Garlyn Zoo off US 2 if you like animals or want to see a tourist trap with animals.
Pictured Rocks National Lake Shore outside of Munising (This one will take a lot of time. It is beautiful, but is best by boat, might be too late in the season.)
Lower Harbor Ore Dock in Marquette is an old iron ore dock.
Old Ford Wood Factory in Alberta. Ford sourced much of the wood for the Model T from the UP. The Ford Family also owns a lot of land in the UP. I don't think tours are offered, but interesting bit of industrial history.
Bishop Baraga Shrine between L'Ance and Baraga if you are into early great lakes explorers.
Get gas in Gaylord or St. Ignace. Between towns in the UP there are very few places to stop, and if there are, the gas is 10-20+ cents per gallon more.
There are places to stop in the lower peninsula, but they lack the character you find in the upper peninsula (UP).
Don't get too creative or adventurous with food choices in the UP. Food quality is hit and miss in the UP.
On US 2 DO NOT go over 60mph unless you want a ticket. The highway patrol is strict about it and monitors. There are a lot of places for them to hide. Also be careful passing on US 2. There are a lot of head on crashes because people are trying to pass on long sweeping curves. Be patient and there will be a passing lane in a few miles.