Good suggestions so far. Besides the hot springs in Thermopolis there is
Legend Rock and the
Dinosaur Museum.
Fort Laramie is not far from US-26. If you are into Cabella's the one in Sidney even has a campground and there is another Cabella's in Kearney.
Guernsey and
Fort Kearney State Parks both have campgrounds. The
Great Platte River Road Archway on I-80 is worth a stop.
The
Amana Colonies are not too far North of I-80 and
Winterset is not too far South of I-80 in Iowa.