In addition to the style of shelf that Drfife showed, I added one of these to the bathroom storage area for storing towels, sheets, etc. I mounted it right over the hangar bar so I have full use of it also.
Picked it up at Walmart for around $12 and it took less than 15 mins to install.
Mike, Sue, Sissy and Little Man
2015 Ford F350 Lariat FX4 6.7 CC DRW
2015 Eagle Premier 351RSTS