I disagree--respectfully--this is either a theft or burglary case and the OP may not be sure whether the DA is seating a jury or just wants him there, just in case.

Take a look at the subpoena and see if it is a trial or a preliminary hearing--then call the DA and see how they suggest you dress. Since it is Texas, I'm gonna guess dress comfortably...but, not in a kilt.

Why? If it is a theft case and you dress too nicely, the jury might think there was no harm. If you dress not so nicely, the jury might be more sympathetic. AND, if you dress in a kilt you might put off one of the members of the venire or the panel. Plus, you are the State's witness. But, this is not legal advice...just a short study of human nature.