While Texas has a hell of a lot of natural resources, trying to break away from the entire commerce cycle and keep growing food ends up getting a bit tricky.
I mean hell you guys can't even produce your own electricity effectively enough to keep people from freezing to death. Even fixing that problem without local suppliers and engineers ends up being pretty damn expensive.
It'll start well enough trying to turn resources from outside the state to local sources. A lot of local small and medium industry will probably be bolstered. But then what happens when the US stops allowing import of cattle. You've got plenty of food, food isn't your problem anymore, but now all those giant farms don't have anybody to sell their goods to anymore. They're going to go from feeding 50 states to trying to feed one state that already has all they want of that product. You can't just f*** with supply and demand like that your economy will s*** itself. You'll be trying to sell oil and gas to Mexico. Your ports will just be packed with tankers trying to find somebody that'll buy your oil, so you can trade for stuff you really need. You won't even be able to fill the tankers fast enough to keep that section of the economy flowing like it is now.
When brexit did it they just got a taste of the pain because all of their trade routes and agreements More or less remained in place just today non-preferential price.
Credit due, you've got a better chance of making it work then just about any other state, but y'all go mad Max before you got it sorted.