What external storage works best on Prius?

I Would like to know how people have added external storage to their Prius and how they would evaluate it.
So far I have seen packs or boxes designed to be lashed to rooftop carriers, packs or boxes supported at the rear using a trailer hitch, and a soft pack meant to be tied to the back of the rear hatch.
I wanted toattach a small hard-sided carry-on to carry overnight clothes or an extra gas can, cooking canisters, etc. The simplest way to attach it to the hatchback that I found was by using luggage belts strung through wire loops attached to the license plate bolts and to a bolt on the side of the hatch:




I have not tested this while driving high speeds or long distances yet.

Anybody have other ideas or experiences?

 

Nah, I found I had to leave the bun off because the total height of the hamburger would cause the top edge of the suitcase to bump against the air spoiler. But then in the interest of longevity and not attracting a crowd of dogs and cats wherever I parked, I swapped out the meat patty for a thin slice of plywood that is screwed to the bottom of the suitcase where the wheels would normally attach. I used a thin piece of foam between that and the bumper, but I am replacing that with the $40 bumper guard strip sold on Amazon.

 

I was looking for info like the mpg effect of different storage because other posts suggested that the roof racks definitely decrease mpg. What brand of hitch and flat tray would you recommend?