I agree it's better than barewords. I almost never use bareword constants, instead always use variables. I think capitalization is enough to remind users not to change them:

package constants;
use strict;
use Exporter;
our @ISA = qw/Exporter/;
our @EXPORT_OK= ($FOO, @BAR, %HASH);
our $FOO = 1;
our @BAR = qw/A B C/;
our %HASH = (A=>1,B=>2);
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