You have to edit 2 files in the folder openerp/addons/product/reports

product_label.xsl for the layout

product_label.xml for the necessary database fields

open product_label.xml and add the following lines:

<loc_rack type="field" name="loc_rack"/>

<loc_case type="field" name="loc_case"/>

<loc_row type="field" name="loc_row"/>

open product_label.xsl and add the following line around 80:

<xsl:value-of select="loc_rack"/><xsl:value-of select="loc_case"/><xsl:value-of select="loc_row"/>