There is a ton of stuff to do in austin.. Check out the local papers. The Austin American Statesman and the Chronicle. You can also read them onlne. They list all of the events going on..
Many free events are available each week. Also, local businesses have events. Central market on North Lamar Shows outdoor movies, concerts,and performances.Check out Hangtown burgers website. Also The Hub...
There are free summer concerts on the lawn of the Long Center, Waterloo Park and lots of other venues. Take a picnic and blanket. The bats at the Congress Avvenue bridge is famous. People come from all over the world to see the largest colony of bats living in an urban setting. You can find the times and dates online,
The farmers markets around town also have free entertainment. The one at The Triangle is every Wed. There is one of those fountains that squirts water for the kids to cool off and they have musicians as well as the vendors selling their goodies.. Remember to take cash. Many of them do not take credit cards.
In the fall many of the local elementary schools hold fall carnivals. They are also a blast and not very expensive.
The City of Austin Parks APRD hae a website with all of the activities listed. Right now the annual Play in the Park is featuring the Music Man. It is wonderful and it is free, Deep Eddy Swimming pool does sat night movies while you swim. You only pay the entry fee, and can take in your dinner.
There are also festivals at the little towns all around Austin.
Have a great time, keep a cooler with water and juice in your car. Also a bag with snacks, sun screen, bug spray, sunhats,blanket and towels is always good to have available when you see an event.