Something like this should work very well. I have a much less expensive version of the same idea that I bought on ebay a few years ago, and it's come in handy a few times.
If your gear gets wet, it's best to leave it out of the bag when you get home. Take the lens off, take the batteries out and lens caps off - whatever you can do to help it completely dry out. Also, carrying a small towel in the car will help.