1. water
2. money (in purse, which also has ID)
3. rain jacket
4. u-lock
On 'normal' 25 mile ride, I'm somewhere within Madison's bus service. All buses have bike racks, so if I've managed to get out of walking distance of a bike shop, I can still get home. And my walking range is about 7 miles, so as long as I have money, I *can* make it home.
Once I'm in the 40-50 mile range, I might start needing more equipment, since then I'd be getting out of bus and bike shop range on many routes.