use strict;
use warnings;
use Data::Dump qw/pp dd/;




package Class1 {
    our %cfg = (a => 1, b=>2);
    sub cfg { %cfg }
};

package Class2 {
    use parent -norequire, 'Class1';
    our %cfg = ( %Class1::cfg, a=>11,c=>33 );
};

package Class3 {
    use parent -norequire, 'Class2';
    our %cfg = ( %Class2::cfg, b=> 222 );
};

pp
  \%Class1::cfg,
  \%Class2::cfg,
  \%Class3::cfg;



# **** THIS DOESN'T WORK

package Class2b {
    use parent -norequire, 'Class1';
    our %cfg = ( SUPER->cfg(), a=>11,c=>33 );
};

pp {Class1->cfg()},
  \%Class2b::cfg;

##</code><code>##

...
package Class2b {
    use parent -norequire, 'Class1';
    our %cfg = ( __PACKAGE__->SUPER::cfg(), a=>11,c=>33,n=>'2b' );
};

pp \%Class2b::cfg;