Or, keeping the xpath expression simple, plus testing element after breakfast menu:

#!/usr/bin/env perl

use strict;
use warnings;

use XML::LibXML;

my $dom = XML::LibXML->load_xml(string => <<'EOT');
<?xml version="1.0" encoding="UTF-8"?>
<restaurant>
   <timestart>0600</timestart>
   <timeend>1030</timeend>
   <city>Boston</city>
   <country>US</country>
   <breakfast_menu>
        <food>
                <name>Belgian Waffles</name>
                <price>$5.95</price>
                <description>Two of ...</description>
                <calories>650</calories>
        </food>
        <food>
                <name>Strawberry Belgian Waffles</name>
                <price>$7.95</price>
                <description>Light Belgian ...</description>
                <calories>900</calories>
        </food>
   </breakfast_menu>
   <edgecase>test after breakfast</edgecase>
</restaurant>
EOT

my $root = $dom->getDocumentElement();

for ($root->findnodes('/restaurant/*')) {
    next if 0 == index($_, '<breakfast_menu>');
    print "$_\n";
}
[download]

Output:

<timestart>0600</timestart>
<timeend>1030</timeend>
<city>Boston</city>
<country>US</country>
<edgecase>test after breakfast</edgecase>
[download]

Note: If you only want elements before breakfast menu, change next to last in the for loop.