[Theeper]

You could make an array of the turn-in items and loop through them. Something like this should work for you.

@items = (1001, 1002, 1003, 1004, 1005); 

sub EVENT_ITEM {
   my $accepted_items = 0;

   foreach (@items) {
      if($itemcount{$_} == 1) ++$accepted_items;
   }

   if ($accepted_items > 0) {
      quest::summonitem(1006);
   } else {
      plugin::return_items(\%itemcount);
   }
}