I have an Osprey Float and wear it really low at the back of my hips, which keeps it in the most aero position possible when I'm in the drops. By cinching the waist strap tightly around hip bones, it is really solid and does not move around at all. Plus this keeps the center of gravity lower than wearing it high.

I don't bother trying to pull stuff out of it while riding -- never occurred to me why you would need stuff while moving.