Get value of variant field in plugin
Something like this should work:

public function init()
{
    craft()-&gt;on('commerce_lineItems.onPopulateLineItem', function(Event $event) {
        $purchasable = $event-&gt;params['purchasable'];

        $myDropdownFieldValue = $purchasable-&gt;getProduct()-&gt;getContent()-&gt;myDropdownField;
    });
}


Relevant event docs: https://craftcommerce.com/docs/events-reference#commerce_lineitems.onpopulatelineitem