I didn't literally mean you have to retreat to your tent or RV to drink, although that would be the surest way to ensure you're not "publicly consuming" your adult beverage.
Most of us have enough stuff on our picnic table when we're camping it'd be difficult to see if someone had a Bud or a Dr Pepper, anyway. Just use common sense and drink responsibly and you'll be fine.
Texas open container laws apply within the parks, so don't pop one and carry it around in your vehicle if you go driving around.