You can make a nice trip out if going to San Marcos - central Texas is very nice...
Suggestion - leaving Dallas, go 281-South and avoid the bulk of I-35 (set a GPS waypoint for the town of Hico). In transit to Hico, you’ll go through Granbury and Glenrose). The drive is much nicer than I-35.
The LBJ Ranch/Texas Whitehouse is in Stonewall, TX only 60 miles from San Marcos. You can step inside of Air Force 1/2 (in Stonewall/LBJ Texas White House).
https://www.nps.gov/lyjo/index.htmFredericksburg is right down road from Stonewall- the National Naval museum is in Fredericksburg - you can touch a midget submarine that entered Pearl Harbor on 12/7/41.
https://www.pacificwarmuseum.orgEven though the glass-bottom boats runs are currently closed, it’s still worth going to Aquarena Springs....right across from the football stadium...
https://www.meadowscenter.txstate.eduDon’t forget the outlet mall south of town - 350 stores in one location..
https://www.premiumoutlets.com/outlet/san-marcos