Here's a link to altitude sickness, it's cause and treatment. I've never had a problem with it more than just feeling tired.
http://www.princeton.edu/~oa/safety/altitude.html
One more thing....glass, you need some decent binos and a good system for carrying them. The regular neck strap gets old quick. I always bring my spotting scope but only use it during the first couple of days of scouting. After we figure out where were gonna hunt, I just carry binos.
I bring boots for bad weather, but use tennis shoes are regular hiking boots as much as possible.