for my $i ( 0 .. $#list ) { 
  $data->{"IS_LAST"} = $i < $#list ? 0 : 1;
  ## ...
}

##</code><code>##

for my $item ( @list[ 0 .. $#list - 1 ] ) {
  process_item( $item, 0 );
}
process_item( $list[ $#list ], 1 );