Most readers here know what a storm cag (cagoule) is, but for those who don't ...
You can put the cag on over your pfd and skirt. Once you have it on, it attaches at the bottom around the coaming over your spray skirt, So I keep mine handy if there is any chance of cool/cold weather degenerating into rain/snow. I can easily put it on without rafting up etc. I actually consider it to be a piece of safety gear guarding against hypothermia.
I agree about the utility of the storm cag.
Ashore, it's great for keeping warm on lunch stops on cool rainy days.
It can be pulled over my PFD and sprayskirt and tucked around my knees, but isn't too baggy or long to prevent moving around.
It really would have come in handy yesterday! I was teaching kayak lessons at the local lake and it was a pretty rainy day, then one of my students decided to go for an unplanned swim. He was fine and warm enough, but I think he might have appreciated the extra layer. Next week's students will get to check it out.