use strict;
use warnings;

use Data::Dumper;

{
    local $/;
    $_ = <DATA>;
}

my $raDataItems =
   [
       map {[split m{\n}]}
       m{(ITEM.*?)(?=(?:\z|ITEM))}sg
   ];

my $dd = Data::Dumper->new([$raDataItems], [q{raDataItems}]);
print $dd->Dumpxs();

__END__
ITEM NO:1
[aaa]
111
[bbb]
222
[ccc]
333
ITEM NO:2
[ddd]
444
[eee]
555
[fff]
666
ITEM NO:3
[ggg]
777
[hhh]
888
[iii]
999