Not that you would necessarily need a full frame camera, I carry along in my travels a couple of Canon 5D3s, 16-35mm, 24-105mm, 70-200 lenses, along with a couple of external flashes, and a tripod. But this is overkill for most people. A second body isn't necessary. You could opt for the less expensive Canon 6D (which is actually slightly better in low light than the more pro and versatile 5D3) along with the 16-35mm ultrawide for architecture/interior and the 24-105mm for general purpose shots. A Canon 430EX II external flash might come in handy as well. A compact tripod also if you're planning on taking night long exposures.
Though if you're going to be travelling with a large group of impatient people, forget everything I wrote and just bring along a premium compact.
