https://comptroller.texas.gov/taxes/publications/98-1017.php

No sales tax on selected emergency preparedness items, such as generators (up to $3000), ladders (up to $300), and a bunch of other things that cost less than $75 (flashlights, batteries, coolers, first aid kits, hatchets, smoke detectors, and more).

You can purchase certain emergency preparation supplies tax free during the 2017 Emergency Preparation Supplies Sales Tax Holiday. There is no limit on the number of qualifying items you can purchase, and you do not need to issue an exemption certificate to claim the exemption.

This year’s holiday begins at 12:01 a.m. on Saturday, April 22, and ends at midnight on Monday, April 24.