This is a good thread.
Some of the DCC will be riding to Milwaukee this summer, a very small run (100-120 miles or so one way) but it should be fun regardless.
BostonTrevor said it right - install different cogs and you got yourself two gears to work with if you need to. One for the flats, one for the hills.
The thing with minimalism - I like this. Indeed, it's like the old days. I think a messenger bag's worth of stuff would be fine. At most I'd add a saddlebag. How far could you go?