My ideas listed below are based from hosting my sister-in-law and her family visiting from Amsterdam several years ago for their first "Texas Experience" ranging from outer space, to the Mexican heritage and cowboy way of life.
Pre Cruise:
An option is arriving a couple of days early and explore the Space Center Houston and area before the cruise.
Post cruise:
Day 1:
Go to San Antonio (4 hour drive) for an overnight and visit the Riverwalk at night and eat some Tex-Mex food.
Day 2:
Go to Fort Worth (4.5 hour drive) to visit the Stockyards, watch a Rodeo, and end the day at a Texas Honky Tonk. On the drive to Fort Worth stop at Buc-ee's in New Braunsfels.
Day 3:
Go to South Fork Ranch (1.25 hour drive). Afterwards depending on the time of the year the State Fair of Texas (SEPTEMBER 30 – OCTOBER 23, 2022) might be an option otherwise a Dallas guided tour.
Of course make sure to eat some good Texas BBQ before going home.