Preferred,
I know that laws like that used to be true years ago, but I find it difficult to believe they still do. Wisconsin has always had fairly liberal laws regarding alcohol (although I don't think we've ever allowed open containers, at least in my lifetime) and we had a fairly major spat with the feds a few years ago about our 18 y.o. drinking age. We had to change it to 21 or lose all federal highway funds. And the feds still pull the same crap every time they want another law changed.
So, at least judging by whats happened here, it seems difficult to believe that Texas would still allow open containers. But, if they are, I know a few State legislators that would be interested in that info.