use Array::Lookup;
my @required_items = qw(apple  orange pear);

@collections = ( [ 'apple', 'pear' ],
                 ['banana']
            );
foreach my $collection (@collections) {
    foreach my $required_item (@required_items) {
        lookup $required_item, $collection, \&notfound;
    }
}

sub notfound {
    my $required_item = shift;
    my $collection    = shift;
    push @{$collection}, $required_item;
}

foreach my $collection (@collections) {
    print "@{$collection}\n";
}