I'm just getting into trail running and besides a good pair of shoes, what is your other must have piece of gear for a beginner?
@K2 I use one of the front bottle holders (Salomon or UD vest) and keep more water in the back instead. That's the best place I've been able to find for it. I'd rather have that than water right there, especially running in and around the Tetons....
You already said shoes, but I would add that the shoes need to be appropriate for the type of terrain you'll be running. I live in PA, and our trails tend to be very rocky, so the stiffer the sole, the better.
The other thing I would recommend is a running pack that will hold your essentials, including a water bottle. I found one a few years ago that fits snugly around my waist, so it doesn't jump around while I'm running. It holds my car keys, iPhone, ID, and a water bottle.