A beer joint is a tavern without the atmosphere, the quintessential drinking hole for those who are looking for cheap beer and good company without having to worry about putting peanut shells on the floor.
A beer joint sells only beer, and maybe some wine splits for the odd times when a girlfriend or wife who doesn't like beer comes in. The food is restricted to snack items, but they can be good. One of my favorite places used to keep a hoop of cheddar cheese you could buy by the ounce and eat with saltine crackers. In the south, pickled eggs and sometimes pigs feet are found in gallon jars on the bar, to be fished out by the bartender and served on paper towels.
Beer joints usually cater to a local clientele, and it may be the only place you see some of your best friends in life. It varies from place to place, but strangers are usually welcomed as long as they don't expect to be immediately included in conversations that have been going on for decades.
In the rural low country of South Carolina where I grew up, gas stations and bait shops often doubled as beer joints. Men would congregate in the shop after work and suck down a few cold ones before heading on home. The more popular of these would sometimes close down the gas pumps and get rid of the worms and crickets and put in a real bar with real bar stools and maybe some tables and chairs. The really fancy places would leave an area of floor open and have a jukebox. It was known that women and even children were welcome and to be treated with respect in these places, but the fare stayed the same - beer and snack food.