Big Zip-Lok or drybag packed as you have described. The Zip-Lok is lighter, cheaper and quicker to open, but not as heavy duty as the drybag. I would take along a smaller camera too so you can always have a decent one with you. Phone cameras are handy but take poor photographs. Anything less than a nice SLR like your 50D is definitely a compromise, but there are some good compromises in the smaller cameras that provide reasonable photos while assuring you will have the camera around when you need it. I wish I could always have my SLR when I am out in the field, but that is not always practical. I love the idea of the small, waterproof/crushproof cameras, but they don't take very good pictures. The Canon S95 is would probably be the current best compact companion to your 50D because it has some of the nice features that more advanced shooters actually use. I use a Sony DSC-H55 which is easy to carry and takes okay pictures and videos, but doesn't compare very favorably to an SLR except in bright, sunny conditions when I am not using a higher zoom. I bought my wife the Sony DSC-HV5V that is an upgraded version of my camera with GPS geo-referencing. It cost me twice as much as mine and has the GPS, higher resolution video and takes slightly better pictures, but she doesn't use the additional features much, and the picture quality difference is not that noticeable under most conditions. I definitely would not spend a lot more money mainly for features you won't use. My Sony is not expensive, but there are more expensive, better performers on the market, like the Canon S95. Best not to buy compact cameras over about 10 or 12 zoom if you want to maintain fairly good image quality. The higher zoom compact cameras have high noise, especially when cranked up to high powers. Of course, if you absolutely need the magnification, you will be forced to compromise the image capture. Just as with lenses, size does count in the camera body with larger bodies often incorporating larger image sensors. Here is a good link.
http://en.wikipedia.org/wiki/Image_sensor_format#Sensor_size I went way past your question, but only because you pretty much had the right answer on the packing anyway. I really just wanted to encourage you to take a smaller camera too if the SLR got too burdensome. Also, it is nice to have a compact camera in your pocket in case you have to drop you pack on a stalk. Good luck on your hunt. Hope you get a nice elk and a lot of good pictures.
Allan