I'm a lawyer who practices in Texas. This is a very murky area of Texas law, in part because there have been very few convictions under that Texas statute and none of them have been appealed (many of them were clearly good arrests without much room for argument) so we don't have the limits clearly defined.
There are basically two definitions of "intoxicated" under Texas law:
1) You have a blood alcohol concentration of greater than 0.08%
2) "not having the normal use of mental or physical faculties by reason of the introduction of alcohol, a controlled substance, a drug, a dangerous drug, a combination of two or more of those substances, or any other substance into the body"
All the officer needs to arrest you and charge you with a crime is to be able to articulate a reasonable belief why you did not have "normal use of mental or physical faculties." He does not have to give you a blood test. In fact, one of the questions on the CHL test is "There is no legal limit of intoxication for concealed carry licensees in Texas" (which is TRUE). So you can be arrested for a violation of Texas Penal Code Sec. 46.035(d) (license holder carrying a handgun while intoxicated) with a BAC of less than .08% (just as drivers have been convicted with a BAC of less than .08%).
As a result, you are running a substantial risk when you choose to drink and carry a firearm in public (either as a CHL or as a non-licensed gun owner carrying in the glovebox of your vehicle), even if your BAC is less than 0.08%.
Let's look at a hypothetical. You have two 12oz beers, which for your weight leaves you with a 0.04% BAC. You roll through a stop sign and are pulled over by Officer Friendly. As required by law for CHLs, you notify Officer Friendly that you are carrying a firearm. Officer Friendly smells the beer on your breath. Officer Friendly, who is a good old Texas boy who went through his hunter safety course (where he was told expressly that guns and alcohol never mix) now has everything he needs to arrest and charge you.
1) You have a firearm
2) You lack normal use of your mental or physical faculties due to consumption of alcohol as demonstrated by your inability to control your vehicle (roll through a stop sign) and beer breath.
Now you may not be convicted on that evidence; but it will support an arrest and it will be every bit as expensive and stressful as a DWI case - and whether that result happens is 100% up to officer discretion and how he feels about guns and alcohol mixing (and its useful to keep in mind that the NRA is very big on "guns and alcohol don't mix" since what the world's largest firearms safety organization has to say on the subject is likely to inform attitudes).
For that reason, many Texas CHL instructors recommend not drinking at all while carrying. Some of those Texas CHL instructors are also licensed Texas Peace Officers themselves which is a big hint on what you might expect from LEOs who aren't licensed CHL instructors.
If you want to minimize your risk to the maximum extent possible, not mixing the two in public is good advice. If you want to find out exactly where the limits of the law are, well, lawyers need to buy .22 ammo too and someone has to be the test case.
