A lot depends on what route you are taking. I would at least do a run on the Mississippi River, lets say from Alton, Il to Grafton,Il. Have lunch at the Winery on the hill, and run back. Also a good "sea trial" on the boat, with pleasure.
There are a number of large lakes not too far off the path--Lake of the Ozarks would be on my list. But you are nearing time of the year, when Northers begin to come down--and it may be blistery...
If you are gong I 80/84, you are not too far from Lake Powell. (Bull Frog). It is late in the season, and there will be few boats/services. Anywhere along this route it may be cold/ice/snow.
If you are going further South, then there would be a different set of suggestions.