Don't drink the water. If that is what the outfitter does, I would take a water purifier. I have the MSR miniworks and it has served me well. It is a good investment/insurance policy against infrequent, but severe infections from drinking creek/spring water.

There are lots of good ammunition choices for the 270. If it were me, I would buy a box of Federal premiums in 140 grain trophy bonded bear claw and 150 grain nosler partitions. Take the one that shoots most accurately. Either will do the job quite nicely out to 200-250 yards. The 270 is not a long range elk gun.

You will need a premium pair of long johns (polypropylene, etc). DO NOT use cotton. The function of long johns is NOT to keep you warm, but to transport moisture (sweat) to outer layers to evaported. When you hike in the mountains, you WILL sweat regardless of how cold. Also, get thin polypropylend sock liners to wear under a wool sock. Anthing else will usually result in cold wet feet and blisters.

Wear your long john bottoms for the ride in. Tends to help prevent saddle chaffing. Take something like ibuprophen for saddle soreness and sore muscles.

If you don't have a good quality sleeping bag with at least a 0 (zero) rating, get one. One cold night and you would pay any amount of money to be warm.

Foods I think of for a pack in hunt: nut mixes, granola bars and cereals, bagels, instant oatmeal, candy bars, etc.