You will love Frank's Diner! The PP was right about it being crowded though. Mornings especially can be really crazy but, that is because their breakfast is so good

They are famous for their Garbage Plate(warning, DO NOT order a whole, it is massive!) but, they have other tasty options as well. We also love their cinnamon roll french toast, pancakes and homemade toast. We've only had lunch there once, the burgers were really good.
In our experience the best times to go are off peak eating hours. It is a very popular place for local business men, retirees and college students who seem to be there earlier in the morning or the standard 12-1 lunch hour. My DD and I pop in at 9 or so and get seated fairly quickly. I don't recommend sitting at the outside tables, the atmosphere is just not the same and the tables are right by the street(car exhaust and eggs don't mix). BTW, they are cash only as the PP mentioned. A full menu with prices is on their website.
While you are in Kenosha you can pop by The Civil War Museum($5) and The Kenosha Public Museum(free). You could also take a ride on the trolley and walk along the harbor. All together they won't take long, maybe 1 1/2 hrs?
As others have said, skip Jelly Belly unless you are a HUGE fan. Seriously. If you do feel the need to go skip the tour, you'll see some video clips and lots of storage shelves(a trip to Costco or Sams would be more entertaining

).
Enjoy your trip