YZEATER,
I've heard good things about this scabbord. see below. it should fit about any scope
Crooked Horn Outfitters Home of the Original Bino System - Rifle Scabbard
Also, If I were you I'd take either the .338 RUM since you want to use it. I would also throw in the rifle you are most comfortable with next. If it's the .257 then have at it. I'd get some Barnes TTSX ammo for it though. After killing many elk with them I wouldn't trust anything else. I haven't heard good things on the accubonds.. Also as some have mentioned before, keep shooting till the elk is down.
Get good clothing, the Rivers west(I've used it) is good if you'll be sitting mostly but if you have to hike you will sweat to death. Maybe look into Sitka, KUIU. if the funds don't allow for it look at the cabelas outfitters fleece or microfleece stuff. Its great for the cost. I'd recommend a merino wool baselayer, I like smartwool but theres also firstlight and a few others. It's soft wont itch and wont start to stink after a day of hunting.
Practice shooting up close, real close like 20-30yds out of breath, and also farther out using the out of breath practice. Most likely you'll be out of breath when shooting. Learn to shoot like that, it could save your hunt. I'd recommend shooting stick, I like the stoney points that you can add the third leg to, or the heavier all in one tripod shown here.
Cabela's: Shooting Sticks & Bipods
You can use these for glassing from using your binos (which you should be doing lots of) and shooting from. They are worth it.
I hope you have a great time and get an elk. Sounds like you have a great start on things. Good luck to you