I manage fine with my Ultimate Direction Diva Hydration Pack on my bike with some clothing in it and a bunch of tools... I'm not sure if it would be big enough for as much as you carry, but without the hydration bag in it definitely. I find it more comfortable than the north face or dakine hydration bags that I have to use for cycling. The dakine ones I hate cycling, but I use them skiing no problem.

My current favorite daypack is the osprey atmos 35 (they have a female version, the aeriel or ariel something like that) - the ospreys have an arched back system which holds the pack away from your back (they just have a mesh that's next to your back, then an arched frame and you put stuff in the pack... It allows airflow between your back & the pack and makes it very comfortable. It's also a light pack. The arch can make it odd to pack depending on what you want to go in there, but what your describing would be fine. I haven't tried it cycling, but I love it hiking. I just usually think it's overkill for cycling for a few hours.