I’m glad that my NX didn’t come with a roof rack, but if it did, I would surely remove the crossbars after reading this article.
I know several “border line” hoarders who have literally hundreds of pounds of junk in their cars’ trunks and could restore some lost fuel efficiency by tossing that stuff 
Not surprisingly, they have a difficult time grocery shopping because there literally isn’t enough room in the trunk for the bags of food and household supplies
In order to get my degree as a Certified Paralegal, I didn’t have to duplicate any of the courses that I took for my B.A. and my M.A., so it was essentially “just” a lot of law courses, a couple of business-related courses, and also a few computer-related courses. In one class, we each had to prove that we could do a Power Point presentation, so I did one on How to Improve Your Gas Mileage.
Naturally, I covered driving patterns/behavior, and the importance of proper car maintenance (including correct tire pressure), but I also included a section titled “Get the junk our of your trunk”. Most of the class–which was mostly younger women–seemed to be shocked by the revelation that the junk they were carrying around in their trunk would reduce their mpgs.
Pfffssttt, some of them would pick up a few MPH from just emptying out their purses… 
One of the most memorable gas mileage tips I ever read came from an article written by the late, great Tom McCahill in which he suggested driving as if there was an uncooked egg between your foot and the accelerator pedal. He also suggested that, when driving a car with an automatic transmission, one should coax the transmission into the highest gear possible as soon as possible.