Pack up camp by about 9:30 am and drive to the famous and beautiful Hamilton Pool. Take time to swim if the weather's warm enough; the water is always cold. Plan about 2 hours there, then stop at nearby Family Business Beer Co. before meandering through the scenic Balcones Canyonlands National Wildlife Refuge. Lake Travis Zipline Adventures is nearby as well if you're looking for thrills. Eventually end in the cute town of Marble Falls; enjoy eating and perhaps shopping there before proceeding to Inks Lake State Park to set up camp for the night. You could of course stay in Marble Falls instead if you wish.
The next morning, backtrack just a couple of miles to Longhorn Cavern State Park and tour the caves. After completing your tour, drive home.
Enjoy the trip!