Could we pack a hash?

Well, yes. pack takes a format and a list of values, and it's rather trivial to turn a hash into a list of values (although you probably want a deterministic order). You probably want something like (untested):

my %hash = make_me_a_hash;
my @key_order = qw[key1 key2 key3 key4];
my $packformat = "ABCDEFGH";
my $packed_str = pack $packformat, map {$_, $hash{$_}} @key_order;
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And you should be able to unpack that as:

my %hash = unpack $packformat, $packed_str;
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