Going to New Braunfels for Xmas

I got the LAST nonstop seat back to Dulles. I mean the LAST as in any flight, any airline.

IAD dec 25 830am --> San Antonio 11:19am.
San Antonio Tues Dec 29 1143am --> IAD 3:55pm.

I rented a car. Objectives: Gruene General Store, Bussey's Flea Market.

Suggestions?