Not sure why anyone wants to use a saw to 1/4 an elk. You can do it all with a knife. A clean bed sheet comes in handy too, you can lay all the meat on it while you are working. I'd suggest deboneing every thing, except the hind quarters first, then put every thing in breathable meat bags and hang them in a tree so that air can get to as much meat as possible to cool. It's not hard to do half an elk, then roll it over and do the other half.
If you're going to be hiking back to camp for help, you got to at least field dress an elk, and don't diddle daley around waiting for help. Leave a note as to your where abouts and situation at camp, and get after hauling the meat back yourself.
The stream of cold water is good, but not all elk fall near a stream!
Any good frame pack should come with a detachable bag, should have adjustments for shoulder width, should be lite, should have a bench that can fold down to support the weight. And bungy cords work well to secure a load.