Milk Krate
Well... I know this sounds dorkie, but I bolted a big wire milk krate to my rear carrier. It is surprisingly light considering the size.
It is extra big - a real metal wire milk crate, not one of those plastic wanna-be's.
It 'aint real pretty, but it sure is convenient to be able to simply throw anything and all things into it and go. Heck, with bunjee cords, I could get a German Shepard into it.
At Christmas, I carried a whole crock-pot full of chili to work including the crock pot, heating unit, and all; along with gifts for my friends and workmates. I didn't even have to put the chili in a separate container and just kept it in the upright crock pot which fit nicely in the milk krate.
What pannier could do that?
It isn't really aerodynamic, but my body is wider that the milk krate and acts as the most imperfect wind-foil.