Someone basic, attached to day by day issues, ruled by the common sense. Not a dreamer or idealistic, not into the creative field or the Arts. Usually connoted with one either without studies or a especial knowledge or intellectual skill. In some context you may use it to express ones singular act, but not the person them self.

someone who can eat a bowl of golden grahams while watching conan o brien on tv.

An grossly overused, idiotic phrase which technically means "one who has no imagination." The funny thing is, the type of people who generally assign this quality to themselves are the artsy-creative type. To many drugs will do that too you.

The quality users are trying to express is: genuine, real.