If you decide to carry an extensive 6x6 setup, make sure whatever backpack you choose fits well. It needn't be a photo backpack (and, in fact, I'd not take a backpack that looked like it might contain photo equipment to a lot of places), but a full MF system tends to be heavy and you'll appreciate a backpack that fits well. I carried a Bronica S2a system in Europe earlier this year, and I wish I'd had a backpack that fit better.
With a little Velcro and some ingenuity, you can make any backpack into a suitable photo backpack.
One thing that I carried and I'm glad I had with me was an Ultrapod. It's a table-top tripod with a Velcro strap on it. It will hold a surprising amount of weight, it can be strapped to any handy pole or railing to provide support, and it takes up no appreciable room in your backpack. In places where a tripod is forbidden, you can often find a place to sit one of these down and get a shot that would otherwise be impossible. Very much a good $15 investment.