I'm not an expert, but apparently transport accounts for only 11% of carbon emissions for food [1], and I suppose it's likely similar for beer. To me this suggests factors affecting production are far more important.

[1] https://news.climate.columbia.edu/2012/09/04/how-green-is-lo...

Best option is to get a refillable growler from your local brewery. Or, get beer from the tap at your local pub.

Growlers go flat too quickly. I typically don't want to consume a half gallon of beer in one sitting.

Apparently there are growler tap kits, so that the growler can be enjoyed throughout the week instead of a single sitting.