A honky-tonk is...

...a 'spit and sawdust' pub - probably of wooden construction, sometimes bordering on ramshackle (falling apart). With little in the way of decoration, apart from maybe the odd license plate on the wall or beer sign, and a jukebox. Usually (in films) in the middle of nowhere - so all the customers (which there wouldn't be any) have to drink and drive to go there.