Cheap pillow cases. Clip the folded over corners and slip in a 1/4" rope draw string. King size slips over elk hind qtrs and regular work well on deer and elk front shoulders. Three to four usually does the trick with both front shoulders fitting in one, each of the hind qtrs in two others. I then use an extra case for the neck and other meat. If you bone out at the kill site, three will get you through an elk without much problem. They are easy to carry and just throw them in the wash with a little bleach when you get home.
They breathe, allow drainage and keep the flys off while in use. A little pepper on the outside my help keep the flys away completely. If one or all are too stained to go next year, they are cheap, buy new ones and wash before packing them.
I sometimes fold and roll them up into a tight ball and zip tie them for easy carry in my day pack. A twist with a small pair of pliers break the tie when you need the bag. I carry a small leatherman for this and other uses. FYI - Trying to break the tie with a knife can be hazardous and can be difficult.
Has worked for me on several occations, but I am sure there are plenty of other bags that work just as well or better.
lkhtr