Boots, sleeping bag/pad, daypack and pack frame have all been mentioned, and good wool / synthetic clothes. These are all critical.
I don't know about the weather around your hunting area, but suggest if rain or snow is a possibility that you also consider a good waterproof or waterproof/breathable jacket with attached hood. Rain gear is so important when you need it that it can mean life or death.
If you want to maximize your hunting dollar, consider doing without some electronics. I know it's borderline sacrilege in some long range shooting circles, but with any reasonable elk cartridge/scope combo you won't need a rangefinder if you are within 300 - 350 yards, and most people should stalk closer if they're farther away than that.
If you are competent with map and compass, you don't really need a GPS.
A folding saw and meat bags are something deer hunters often don't think about. Saws are handy for more than just sawing bone and are lighter than a hatchet.
I don't hunt elk without a cow call in my pocket. I can't count the number of times I've calmed an elk down that I've accidentally bumped into when sneaking around and pretending I'm being quiet. If you can't be quiet enough - sound like an elk.
You mentioned you have a good handle on optics, my advice is once you get into good elk habitat, to use your binoculars more and boots less.
Good luck!
Awesome post, however I can use a map and compass and always have mine in my pack. I seldom use it, after buying a good GPS though. I love my GPS, it's an essential part of my equipment. We should go into great detail of what's hidden inside our day packs. What you put in there is as critical as anything else about the hunt. Here's a list of what's in mine:
1. Waterproof matches and lighter.
2. Nylon rope (about 20')
3. paracord (about 20')
4. Knife set with saw. I prefer the 2 knife and saw kit, made by outdoor edge, called the Kodi Pak knife set.
5. Small first aid kit
6. Map of the area.
7. Lensatic compass
8. T.P
9. Food: Jerky, roasted almonds, m&m's, dried fruit etc. etc....
10. Water
11. Waterproof jacket
12. Warm hat
13. Gloves (water proof)
14. Small thing of electrical tape
15. Batteries for flashlights and GPS (at least 2 sets for each)
16. Headlamp (2)
17. 2 small led flashlights
18. Disposable package of field dressing gloves.
19. Small whistle
20. Small packets of anti-fog glass cleaning wipes.
21. Emergency blanket.
22. Small knife sharpener.
23. GPS
24. Small camera, if you are that worried about taking pictures of your critter like many here. My GPS has a camera built in, so I don't pack a separate camera around...
Am I missing anything??? I definitely agree about using your binoculars. I am always wearing mine and use a semi-compact set (8x32 mojaves) that weigh about a pound and are comfortable enough that they are barely noticeable. This is what's in my pack. Others may vary.
As far as other gear you need:
1. Extremely reliable
rifle #1!!338 win mag2. Scope that isn't going to crap out on you during the hunt.
3. Excellent pair of lightweight binoculars.
4. Laser range finder is only necessary if you plan on shooting past 350-400 yards. Most of my elk have fallen between 30-100 yards so a LRF has never been part of my list of "needed" gear for elk hunting. However, it all depends on the landscape, where you are hunting.
5. At least 2 good pairs of WELL BROKEN IN boots. Switch them out every other day if you are hunting in solid rain or snow.
6. As someone else mentioned: Kenetrek gaiters or similar gaiters. You'll be glad you bought these.
7. Good comfortable warm socks.
8. Good lightweight COMFORTABLE pack frame.
9. Insulated Gortex pants if temps get down near freezing.
10. Long johns (top and bottoms).
11. My elk hunting partner and I have both started wearing those camo baseball caps with LED lights in them. Those are awesome for hands free lighting when gutting out a critter or even walking out of the woods at night. I've used mine quite a lot in the last few years..