One of the most important things to pack in your suitcase is space, so you can bring back literature, sales kits, etc. from exhibitors you meet during the conference.
And then there are various promotional items you might pick up. I’ve got four kids, so if an exhibitor has a stuffed animal or other tchotchkes, I need four to maintain harmony at home.
I suppose some germaphobes only wear their undergarments one time and then throw them out. If that’s the case, space will magically be created.
But for everybody else, leaving some extra space is useful so you don’t have to fight your luggage to fit everything.
The way I keep my clothing organized in my luggage is with packing cubes. Get some of those if you are not already using them.