A subject near and dear to my heart! Wild weather is the rule here. For wet, you just can't beat plastic bags. You can't buy anything, no matter the cost, that works better. The bigger the bag, the better. I have a collection. Bed, Bath, and Beyond uses humongous bags -- to name one. The bags dry cleaning comes in are good, if you're careful with them.
What you need to do is this: In the middle of the bottom of the bag, cut the smallest opening that fits a filter for your lens, and then tape the cut edges of the bag all the way around the filter. When the filter comes off and on, the bag comes with it. You do all your work with the camera inside the bag. Only the filter gets wet. You can also tape the bag to a metal lens hood/shade and then just make sure you don't point your camera into the rain.
I don't use a camera that needs a battery when it's really cold. When I'm shooting in the snow, I keep my exposure meter in a pocket on the inside of my coat. Body heat keeps it working fine.