The possibility to select the content of the package as you can see on the Virtuemart image.
In the Language file you can find it in en_GB.com_virtuemart.ini
COM_VIRTUEMART_UNIT_NAME_xxxx
COM_VIRTUEMART_UNIT_SYMBOL_xxxx
it reprecents the content of a package.
"a bottle with '100 pils'"
In next version of Store Manager, which will be released tomorrow, this field will be available. Please, check screenshot: http://screencast.com/t/PPO2Imhqz
Let us know if any other questions occur!