no better way to sour meat than to leave it in plastic bags for very long at all.. I use canvas game bags. by the time you bone and drain, or quarter your animal, and let it hang or drape on a log or rock between your trips with your pack, it will be dry enough to pack cleanly.. besides, who wants a pansy-clean backpack? any pack worth owning can be washed clean. and any pack worth taking hunting can be used for its purpose!!
I just use the realy heavy plastic bags (hint: go to the airport and get some of those heavy ski-transport bags) plastic just to pack it in the backpack while hiking, then into muslin cloth sail cloth, or light white canvas to drain and dry.. then into coolers at truck or airstrip. If you use plastic, and need to store it for any time at all, make sure that no liquid accumulates.. it is a bacterial soup kitchen.
Before I broke down and paid 6 bucks apiece for the reusable canvas game bags, I used pillow cases for years... one pillow case will hold all a person can carry and leave enouth material to tie up and hang form a meat pole..