I don't really know what proper etiquette on this is either, since my etiquette book was written before take-out places were common.
However, I honestly don't think tipping for takeout is fair...I understand that the people putting orders together may not be getting paid much, but
they should be, especially if a place is takeout only. I can see tipping for a regular restaurant's curbside service maybe, but not for takeout. That, to me, seems dumb.