Don't ever put your game meat in plastic bags unless it's well below freezing. Plastic doesn't allow the meat to breathe and will promote bacterial growth. If you want light weight game bags these are the bomb...

http://www.pristineventures.com/products/game-bags.html

They're light, take up very little pack space, and they're washable so you can reuse them. I've used them for five or six years now and I won't go back to the old cloth type.