I wouldn't use an anonymous sub for that first bit. Maybe it's one case where map in a void context would work.

On the other hand, if this is something you might want to do later, there's no reason not to turn it into a function itself. Regardless, here's the damage that Dominus may cheer and merlyn will jeer:

$header{'Number of Drills'} =
    (map { $total += $_->{count} foreach (values %{ $_->{tool} });
        $total } @drill_arr)[-1];
[download]

Yuck. :)

Update: I spent too long getting this to work and forgot about do. Don't hate me because I wrote perverse code. Just live and learn.