I'm looking for a backpack just large enough to hold a one-man tent (18" maybe) plus some smaller things. I also want the small size because it will blend better in the city. Maybe I'll stay overnight in the wilderness at some point, but it's mainly for suburban campgrounds within two miles of civilization (stores).

I want it to be very water resistant so I could feel safe putting my briefcase in it and walking several miles to work in the rain (not sure I'll actually do this, but I've seen waterproof roll-top models so I figured I should get something like that just in case).

I may take 15-20 mile walks, so I want the ventilation (for my back, not the contents). Any ideas?