Food and water are a must. East Cross Creek is a good place to fill your water bottles. Being well-hydrated is crucial, especially at altitude. Bring iodine tablets or a water filter. A guidebook and map will keep you from wandering into Neverland.
Numerous guidebooks line the shelves of Colorado bookstores and mountaineering shops.
Some books give fine details, but others are rather vague so choose wisely. I used Dawson's Guide, The Colorado Fourteeners, and found it to be comprehensive and easy to understand. Clothing is more of a personal preference, since some think 50 degrees is hot, while others shiver. Photo ops abound at every step. Be sure to start early in the day, both to avoid adverse weather and to see that incredible sunrise.