Our "suitcase" is a durable, carry-on size backpack bag from Rick Steves.
On the first layer we'll stack any clothing that we don't roll. I don't bother rolling jeans; I just fold them in half and they fit just right. Then the clothing rolls go on top. If you have really heavy stuff like boots or really big guidebooks, they need to go in the bottom of the bag (the lowest part if you've got the bag on your shoulders). You don't want your bag to be top-heavy--it won't sit well in baggage racks on trains and you don't want the heavy stuff crushing your shirts every time you plop your bag on the floor.
