For my 600k, I got a size medium Ortlieb bar bag and a large Ortlieb saddle bag. Both are waterproof and I can get stuff out of the bag easily on the fly:



The tough thing was figuring out how to attach the lights which would normally go on the bar. Here's a picture where the bag doesn't look so overwhelmingly big:




I didn't really notice any change in handling. It worked great!!