If you can bone out and hang your meat in the deep dark shade the day you kill the Elk and then let it hang that night you will be in good shape
If it is blazing hot during the day, you can wrap the meat with your sleeping bag. This will keep it cold while your packing it out in the mid day sun. I have never had to do this though. Has anyone? How did it go?
If I ever do, I will put the meat in my Kifaru meat baggy, then drop the meat baggie in my synthetic sleeping bag, wrap it up with the rest of the bag and put it in my pack. In my experience after I let the meat hang for a night, it doesn't drain/leak much if at all. Especially if it stays cold.
Last season, after letting it hang all night I put my Goat meat in a meat baggie and then in my pack. It was a 8.5 mile pack out so it was in there all day and it didn't leak. This was the first few days of October and it was upper 30s at night and 70s that day.