I was actually about to reply with something similar myself before I noticed there's three cases to distinguish. FWIW, here's my previous take - which adds a comma even when there's only two elements in the list:

sub serial {
    my $last = '';
    ($last, $_[-1]) = ($_[-1], 'and ') if @_ > 1;

    join(', ', @_) . $last;
}
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Makeshifts last the longest.