You might go back in the archives and find a thread posted by Greg/MO on his trip to Colorado. Lots of good advice on there. I'm assuming you will hunting in the mountains at high elevation? You will likely experience a headache the first day or two, as your body tries desperately to build red blood cells. You need to drink about twice as much water as you are used to; and be prepared for very rapidly changing weather conditions by dressing in layers.