Daypack - Alternatives to Lowepro ComouDay Photo 250?

Very high quality and flexible bags because of the removable camera inserts that come in different sizes.

I have the Loka and absolutely love it.

It should fit your requirements, except it's not necessarily fast access to the camera, as it doesn't have a side entry pocket and is instead rear entry.

http://fstopgear.com/en/product/mountain/guru