Shouldering my way through a massive crowd on the Riverwalk after an AF BMT graduation is not my idea of fun. Weekend evenings if you are early enough can be OK, but it gets crowded and drunks abound.
1. Alamo, and the Cathedral: Not only history of the fight for freedom, but free guided tours by the Sons of Republic of Texas. The Cathedral has the remains of James bowie, David Crockett and Col Travis, in a crypt at the front entrance. Between the two sites in the Presidio, all of which played important parts in the Siege of Bejar and the Battle of the Alamo.
2. Menger Hotel: Not only Teddy Roosevelt's Rough Riders, but impressive architecture in the older part of the hotel. Fun shops along the front facade.
3. The Museum at Ft Sam Houston is closed right now for a move, but has incredible history of the region.
4. Schlitterbahn, a water park in New Braunfels. You can also tube down the river through town.
5. Gun Show. There is a gun show EVERY weekend somewhere in San Antonio.
6. Canyon Lake: For a lazy day on the water, go to the Army facility at Canyon Lake, and rent a pontoon boat or fishing boat. Bass. Lots of Bass.
7. Imax at the River Center Mall. (near Alamo) It has a great movie about the Alamo, as well as whatever is the hot ticket for 3-D, Imax currently released. (currently Guardians OF The Galaxy")
8. Bass Pro: Big Bass Pro out at the mall called the Rim. I-10 north. Also another IMax theater out there with a restaurant and bar inside. (have a pizza, then take a frozen marguerita into the show. Wow)
9. Brackenridge Park, Zoo, and mini-train.
10 Sea World, and Fiesta Texas/6 Flags.
Stay out of the PX or you will be standing in line with 4,000 other AF parents and their graduating Servicemen/women.
Depending on your tastes, 11. Mi Tierra is a great Mexican Food Restaurant. Either go early (just before 5 pm, or very late, like midnight breakfast) or you will wait in line there too. 20 bucks gets you two songs by Marriachis. Wait for the larger band rather than the two guys. Large Shopping center for imports.
12. The Majestic Theater: Smokey Robinson will be there August 20. They have concerts, major plays (we saw Les Miz there), and other activities. An incredible theater building. Worth seeing anything there, just to experience the building.
Good luck.