I haven't used one but have thought that a kid's flat plastic roll-up snow slide would be easy to carry and provide a tough sled for sliding an animal.
I used to skin most predators on the spot and only carry out the rolled up hides. It is amazing how fast and easy a coyote is to skin if done within five minutes of his demise. He will be signifcantly harder to skin after 30 minutes.
For those taken out whole, I carried a big contractor trash bag to put the critter in and slide/drag it on the snow. For whole deer, or quarters of elk, the hair side slides well on an unskinned critter. Drag it so the hair direction aids the slide, and looping a half hitch over the nose for a direct pull makes for the easiest drag on whole deer. Use a deer foreleg cut off as a drag handle.
edited a bit for clarity
