You may have read about the Dr. Bronner’s Soap case here. Well, here is another case of the cops mistaking soap for hard-core drugs: http://www.rawstory.com/rs/2013/12/16/charges-dropped-for-ny-pair-after-a-month-in-jail-when-cocaine-proves-to-be-soap/
It is almost never a good idea to consent to a search. And friends don’t let friends drive with an open container of soap.