decent, fine (esp. AmE), good, honest, law-abiding
common, everyday, normal, ordinary, plain (AmE), regular (esp. AmE)
It's the ordinary everyday folk who come to shop at this market.

humble, simple
friendly
rich
poor
working, working-class
elderly, old
young
black, white
men (usually menfolk)
He described the customs of the menfolk of his family.

city, country
places that appeal to city folk

local

sb's folks (= someone's parents)
I am going to visit my folks during the holidays.

the folks back home

Folk is used with these nouns:
art, artist, belief, costume, culture, dance, dancing, festival, hero, magic, medicine, melody, museum, music, musician, myth, religion, remedy, rock, singer, song, tale, tradition, tune, wisdom