There are many factors to consider for "optional" gear.
Trekking poles have become a standard for me when I hike long distance with a heavy pack- they save my knees and help with balance on the downhill. That being said, I managed hunting without them for 25 years without a second thought. You may not need to take trekking poles with you as you can usually find a set provided by nature if you decide you want some along the way.
Elk decoy: No experience with them, but a few "experts" say they can help.
I would say both items will depend on how you hunt.
If you're carrying a 50-60 lb pack all day for several miles, trekking poles would be a big help. If you're planning to pack the elk out 5-6 miles by yourself, again, they would help. If you're hiking a 40 lb pack into a spike camp and hunting light and mobile throughout the day, they might be unnecessary weight.
If you're hunting in an area that is conducive to decoy use and you're doing a lot of calling, decoys work incredibly well. If you're hunting thick brush, it will likely be extra weight and bulk you don't need.
Both items can be found very lightweight and mobile (less than a pound each). If you recognize a need for them, I don't think you'd be too weighed down by bringing them with you, and they could definitely provide some advantages...
i went with a walking stick its extendable and has a removable top cap threaded to attach your camera or spotting scope or nocs your choice on what you choose to use or nothing at all at first i was hesitant . but man my god how nice it was especially going up and down