You can purchase certain emergency preparation supplies tax free during the sales tax holiday. There is no limit on the number of qualifying items you can purchase, and you do not need to give an exemption certificate to claim the exemption.
https://comptroller.texas.gov/taxes/publications/98-1017.php
http://www.statutes.legis.state.tx.us/Docs/TX/htm/TX.151.htm#151.3565