Went last week with three friends. Absofreakinglutely amazing, and I agree, better than any IM finish. We stayed at Bright Angel Lodge and did the round trip from there, which I think was logistically best (no mules ahead of us). We started at a little after 5am and finished a little before 9pm, with breaks. The Bright Angel Lodge has a restaurant which is open until 10. This was so much more enjoyable than fast food or the emergency food I had in the car. The GC website lists which water stops/sources are on, and supposedly all are turned on as of 5/15.
Nuts/bolts of what I carried:
I'm the second one:
3L camelbak bladder in a pack
Small pack of survival supplies (space blanket in particular) (this is a BACKCOUNTRY hike/run, not a supported race)
Clothing appropriate for starting temp, and whatever it's going to be in the middle of the afternoon at the river (add 20-25 F to the predicted South Rim max temp.)
One more layer of clothing than you think you need JIC
30 or so scoops of tailwind, added to 2 bottles in a vest.
3 Clif bars
Extra socks.
Gaiters
Sunblock, sunglasses.
Hat.
Headlamp and backup headlamp. You NEED one that works.
Foot/blister care supplies. I'd recommend triple antibiotic ointment with anti-pain stuff. Money if you need.
Optional:
Trekking poles--I only used on descent/ascent of South Rim, but some use the whole way.
Hand held point and shoot camera that takes RAW images instead of just JPEG. If you care, get the depth of color/detail that allows you to take really great photos.
NSAIDS. If you would consider using.
Unless you've done a whole lot of vertical, particularly downhill, be cautious. Your legs can only handle so many eccentric contractions. We walked the first 4.1 miles toward the river and shed our extra stuff before starting to run, and still had a bit of a slogfest for the last couple miles. The two members of our party who had done 100 milers said that this run was every bit as hard, if not more.
Enjoy!!! Best run ever for every one of our party.
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Hard work beats talent when talent doesn't work hard.