This will not load all the keys in memory, which may make sense for large hashes:

my $last = each %hash;
while (defined $last) {
    my $next = each %hash;
    if (defined $next) {
# $last is now set, but is _not_ the last, do what you want with it
    } else {
# $last is now _the_ last, do what you want with it.
    }
    $last = $next;
}
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Liz

Update:
Removed next;, leftover from a previous version, not needed with this approach.