I like to pack light when traveling no matter what. For car travel or overland specifically, this means getting as much as I can into the smallest space possible usually, and most importantly trying to plan and anticipate what will or may be worn at any given stage of travel. My preferred method is rolling each piece of clothing and stacking like sausages in large zip lock bags then compressing as much air out as possible. All this gets inserted into some dry bags (I have several of
THIS brand in different sizes from 5L to 55L) that I can either keep on board or put in one of my roof cases out of the way. I like to put one whole outfit in a bag if I can, shirt, pants, underwear, socks and a sweatshirt or button up shirt. It's also nice to be able to trade the clean for the dirty in the bag you just used and keep the scent fresh in the truck :). Just what I like to do, by no means an advanced or scientific method haha.