There is a militia, usually referred to as State Guard and several states have a Naval/Maritime regiment, including Texas[0]. Unlike the National Guard, the State Guard regiments are under the Governors command only.
There is also the Public Health Service Commissioned Corps[1], which have other public health roles, in addition to deployment during natural disasters. The PHSCC deploys with the Coast Guard for sea duty. USA Freedom Corps[2], and AmeriCorps[3] play a role in disaster response.
Team Rubicon[4] is a group of veterans that deploys in disaster response. I think they have small boat capability.