Maybe this is what you want:

#!/usr/bin/perl

use strict;
use warnings FATAL => 'all';

use 5.009_005; # or MRO::Compat;


package MyClassDataHelper;
{

    sub get_all_class_data {

        my $invocant = shift;

        my $class = ref( $invocant ) || $invocant;

        my @all_class_data;

        {

            no strict 'refs';

            for my $package ( @{ mro::get_linear_isa( $class ) } ) {
                next unless defined *{"${package}::get_class_data"}{CO
+DE};
                push @all_class_data, $package->get_class_data;
            }

        }

        return @all_class_data;

    }

}

package MyClass::A;
{

    use base qw( MyClassDataHelper );

    sub get_class_data { return 'MyClass::A data' }

}

package MyClass::B;
{

    use base qw( MyClass::A );

    sub get_class_data { return 'MyClass::B data' }

}

package MyClass::C;
{

    use base qw( MyClass::B MyClass::A );

    sub get_class_data { return 'MyClass::C data' }

}

package MyClass::D;
{

    use base qw( MyClass::C MyClass::A MyClass::B );

}


# Tests

print map { "$_\n" } MyClass::D->get_all_class_data;

# Output:
# MyClass::C data
# MyClass::B data
# MyClass::A data

print map { "$_\n" } MyClass::C->get_all_class_data;

# Output:
# MyClass::C data
# MyClass::B data
# MyClass::A data

print map { "$_\n" } MyClass::B->get_all_class_data;

# Output:
# MyClass::B data
# MyClass::A data

print map { "$_\n" } MyClass::A->get_all_class_data;

# Output:
# MyClass::A data
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