Were you wanting airports with only grass, or that only have fuel? I've made a few grass strip tours and have researched grass strips in the midwest and other areas east of the Rockies. I have a few suggestions after looking at your route.
The airport at Ashland, KS (K58) has two grass runways (used to have three...don't know what happened to the other one). They supposedly have fuel now, but you would have to call and check. For two weeks in May, an instructor has acro camp based there. If you want to walk to town, there is a museum with Harold Krier's airplane, but not much else in the way of aviation stuff.
At Beaumont, KS (SN07) is a grass runway on the edge of town. You taxi to town on a small paved road, stop at the stop sign, cross main street and park in the grass across from the Beaumont Hotel for a meal and/or a room. No fuel there. A cool place.
At Miami County Airport (K81) near Paola, KS they have a grass and a paved runway. Good BBQ restaurant on the field and fuel available. I fly up there a lot to eat and meet friends.
Gardner airport (K34), a little bit north of (K81) near Olathe, KS has two grass runways, as well as a paved runway and decently priced fuel.
Antique Airfield near Blakesburg, Iowa (IA27) has two grass runway. I got a tour of their cool museum the day I landed there. They have a huge fly-in once a year. Normally no fuel available.
The Amana Colonies in Amana, IA (C11) is an interesting place to visit. Grass strip is on the edge of town within walking distance of great German restaurants and neat B&B's. No fuel. The B&B came to the airport to get me after I called them.
There are a few fly-ins (one of them is the week before Airventure) at the grass airfield at Brodhead, WI (C37). It has three grass runways, but no fuel reported.
On your route, there are other grass fields near small towns where you can walk to a local diner to eat, but I didn't know if that was the kind of airfield you were looking for.
I can post websites and/or photos for some of the airports I've listed, if you're interested in any of them. There are a few other airports that I could also suggest, depending on your criteria.
Sounds like you have a fun flight planned.
