My family is involved in a lot of sports. One that keeps us busy through the entire winter season is hockey, played by both my son and myself. My son participates in a travel league, so several times a month we're on the road for half a day to a tournament. While our vehicle is a respectable size, it seems we never have enough room for all his sports gear plus the luggage we need to carry clothing, toiletries, entertainment for the trip, and a few edible items.
Fortunately, we have a luggage rack which we use to abandon. The luggage rack protects the roof of the truck from scratches which could possibly be caused by luggage zippers, wheels and handles. The rack consists of long bars which are perfect for the straps we like to use to tie down equipment.
After determining what we'll need easy access to during the trip, we load the top of the truck up with the remaining items, usually the suitcases. After settling the cases down, I usually try to wrap a small tarp around them in case we run into some weather. While it won't make things waterproof, it will keep most items from being too saturated to wear. My spouse and I get on either side of the truck and use the straps to cinch the luggage down to the roof with the racks as anchor points. Just be careful if your straps have s hooks or metal fittings on the end, you'll want to tie off the ends so that when you drive they're not knocking on the roof.

If you survive hours in the car with your family (and I hope you do!) then when you reach your destination, it's pretty easy to unload the vehicle. If you don't have running boards then be extra careful stepping in the door frame to reach up to the roof rack.