Despite the English meaning "snack" bars or establishments in Japan are actually places where guys pay money to talk to pretty girls.
Usually a flat rate is charged by the hour during which patrons can drink all they want for free and talk to the girls.
Usually no touching is allowed.
Some snack places the girls wear very little and occasionally nothing at all but most places they just wear normal (or sometimes seductive) evening clothes.
But, as I say, usually no touching is allowed in snacks.