In response to this the California governor recommended that people wear double masks

I certainly hope stores don't try to enforce that one. I personally don't think the government should ever have made a mask mandate (of course the legalities and "enforceability" of such a thing is another debate). It should be up to the private businesses and institutions (like schools) to require it.
In general, I don't think the masks do much. I wear them to be polite in certain situations and when I'm required to, but I don't wear them outside in general. I certainly am not going to wear two!