class Coupon extends Eloquent {

    public function cities(){

        return $this->belongsToMany('City', 'coupon_cities', 'coupon_id', 'city_id');
    }
}

Coupon::with('cities')

$coupon = Coupon->first();
$coupon->cities()->get([your columns here]);

Coupon::with(['cities' => function ($q)
{
  $q->select('column', 'column2' ...);
}