2 of everything is a good idea, but not often practical, or possible. Two knives, two pair of boots and gloves, two sets of orange is always with me. Often one for cold and wet and one for moderate. Most of the big items have been mentioned, so these are only add-ons.
I completely de-oil/degrease my guns. Oils smell, elk don't like it. A microfiber towel in your pack is a great idea for wiping off, drying off your gun in case it snows or rains. A silicon cloth or clp wipe is good for when you are done and heading home...wipe down the rifle.
A bone saw of some sort. I have several, but unless you have a guide who is field dressing for you, you will need a sturdy saw.
Frame pack, game bags, 18x24 ziplocs, freezer tape and a sharpie, a dozen nitrile gloves, pen, zipties. Depending on where you get an elk, you may be packing it out. Game officers are writing tickets for waste of meat. If it is going to be warm, coolers packed with blocks of ice in camp. I have fully butchered elk in the field and the small cuts (tenderloins and ribeyes) I put in the large ziplocs and label them. Also use those for hamburger scraps and chunks. Large groups off of the quarters in the game bags so they can be lashed to a pack and carried out. I have packed out a 320 point bull 4 miles by myself...took two full days. Packed ice in after first trip out. Nitrile gloves for gutting, pen to sign your carcass tag after kill, zip tie to attach the carcass tag. I put a short pen, 6 gloves, zitptie in a small ziploc in my pack, times two.
Tip, if you kill an elk in deep, take off your innermost shirt and after you have tied up the elk as good as you can, tie the shirt to the elk. It will stave off most animals for a day.