my $key_fields    = [ qw( trade_ref sec_code lot of other fields ) ];
my $copy_fields   = [ qw( item_period other fields) ];

my $audit = {};

@{$audit}{@$key_fields}    = @{$item}{@$key_fields};
# $item is a hashref with some but maybe not all of the
# above fields defined
$audit->{$_} = $item->{$_} || '' for @$copy_fields;