The bigger picture would help a lot because hand parsing HTML like that is heading for a world of pain.

That said, and without knowing how the code fragment fits into the bigger picture, something like the following may help:

use strict;
use warnings;

my $str = 'Lumber:</td><td align="right"><b>10;';
my $str = 'Lumber:</td><td align="right"><b>10;';
my %hits;

++$hits{lc $1} if $str =~ /(lumber|clay|iron|crop):<\/td><td align="ri
+ght"><b>\d+/i;

print join ', ', sort keys %hits;
[download]

Prints:

lumber
[download]

Note in particular to use of a hash instead of a bunch of manifest variables.