This is such a great question!
I travel ALL the time and always struggle with what to bring, just in case.
Of course, because the gods on Mt. Olympus don't always smile on me, there have been waay too many clouds, sunsets, people, scenes, etc that have passed before my unrecording eye.
So now I take a Mamiya 7 almost everywhere. I can use faster film (d3200 at 1600 is sharper and better than d100 on 35mm) and as long as I can stabilize the camera enough, the pictures are just about as sharp as with a 4x5, up to about 16x20. Of course there are no movements but at least I get the shot. And because of the bigger frame size I need only carry one lens and can crop pretty considerably and STILL get more image area and smaller grain than in 35mm.
Just last week it paid off. I was working in Philly and drove past a house with a statue of The Virgin Mary out front. It made for a hilarious photograph, complete with a caption about how I somehow managed to beat the throngs, pilgrims, and lepers to the apparition!
PS One suggestion that I have been meaning to try...a Holga. All the bennies of the larger frame noted above, plus a pictorial effect, plus it's probably lighter than any non-disposable camera of any kind.