There was this TV show, I think it still runs, I used to sneak in on Saturdays called "Sabado Gigante." It was some crazy music/game show on one of the Spanish channels that featured, among other things, hot latina chicks dancing in bikinis.
Yeah. Anyway, this Saturday you probably shouldn't be sitting around watching bronzed, bikini-clad boricuas on Telemundo because there is enough BMX in a 40-mile radius to fill your time.
First, San Antonio has the 2010 James Jam. I think it starts around noon in the Harry Wurzbach ditch. Peep the flyer here http://theyaintready.wordpress.com/2010/07/01/james-jam-update/ (NSFW. Don't say I didn't warn you.)
Second, The Ultimate Male is throwing an impromptu screening of the new United flick, "This is United," at the T1 ramp in Austin. The video starts when the lights go down around 9:00, but you are invited to ride the ramp before. Flyer below.

So, start your day at 10:00 AM with some Coronas and breakfast tacos down in San Antonio. Jam at 12:00 noon. Bounce out at around 4:30 PM to get to Austin before 6:00 PM. Ride the T1 ramp, chill with bros, and peep the United vid. Then stroll West down 6th for some cocktails. Fuck yeah.