I keep a point-n-shoot in an open pouch on my tank bag. All the camera's knobs are taped down so they don't get bumped and mis-adjusted to the wrong setting accidentally.
On a straightaway I can slide my left glove off between the seat and my crotch, withdraw the camera, shoot, put the camera back in the pouch and get the glove back in pretty quickly. I am prepared to drop or toss the camera to the ground instantly should I need my left hand to control the bike.
I keep a better camera in a tragkorb for higher quality roadside pics while off the bike.