....
my $mech = WWW::Mechanize->new(agent => 'Windows IE 6');
my $url = "https://www.somesite.com";
$mech->get($url);

# This next line prints, to screen, the value as expected
print "Value: " . $mech->field('sessionid');

# These next 2 lines prints nothing!
my $sessionid = $mech->field('sessionid');
print "$sessionid\n";