I tend to always use a hydration pack. I'm coordinated enough to drink through a tube, I'm not so sure about bottles on the bike, I use a frame pump, so having 2 bottle cages isn't possible, adn I definitely use more than 1 bottle on some rides.

I;ve got the Deuter Race X Air I with 3 Liter Hydration Pack:
http://www.altrec.com/deuter/race-x-...hydration-pack

No, I don't always fill it with 3 liters, it depends on how long I plan on riding - all day, yeah, I'll fill it up. halfway or less if it's just a short ride.

The nice thing about this one is that the frame of the pack arches the pack away from your back and there's kind of a mesh area that goes directly against your back - so you get airflow back there & no sweat.

I also don't really have handy friends that live near by that I can call and say, hey, come rescue me... So I do tend to keep it packed with whatever I think I might need worst case scenario. Cooler weather it'll have an extra wool layer, it always has a light windbreaker/rain shell, arm & leg warmers if that's necessary, some cliff shot blocks, cliff bars, spare innertube, some first aid stuff, lights, and tools.