For me, going out with just one lens works really well when I know where I am going and have my mind set on that particular focal length. Even better if I know what I will be looking for. However, if I am traveling to a new place I don't know much/enough about, I take at least three lenses with me, usually more. Once I am familiar with the place and know what to expect, it's easy to pick one lens (or two, or three) and not miss others. So... more or less standard answer - two in the 20-35 range, a 50ish, and something longer (85-200). Two bodies sounds good too, especially if there is a serious risk of someone important asking to hold the camera for more than 5 seconds.