According to the Transportation Security Administration (TSA), airplane passengers flying in and out of the US can travel with an unlimited amount of alcohol in their checked-baggage, as long at it's under 24% alc/volume (48 proof) and fits within standard weight regulations. Seems simple enough, but when it comes to packaging that wine or beer (most are below 24%), things can get a bit trickier. Here are few different packaging regulations from various airlines.
Remember, when flying internationally, wine regulations will differ according to each individual country's customs. Be sure to look into the regulations of the country you are visiting before flying!
Photo courtesy Jeff_Werner via Flickr/CC