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?
A running vest! Get fitted for one or you might deal with chafing (REI can probably help with that!), but a running vest makes you self sufficient on long runs in the woods! You can carry your food of choice, water, extra clothes, your cell phone, etc!
I would also say good bug spray and sunscreen. Pick one that will repel ticks and make sure to test on your skin a day before for allergies. Also some type of head gear to keep bugs out of your hair, Buff's are great for multi-purpose use. And finally, a small light to put on your back so people can see you. The trails can be dark even during the day and if you would fall it's nice to have that flashing.
Sorry, wrong thread.
Agreed. Running is an inherently minimalist sport, and that is part of what makes it good.
I second the vest idea - it gives you options for changing conditions. I also like a light pair of gaiters just to keep the trail-dust and hemlock needles out of my socks. In winter I have a heavier pair (made by Ice Bug) that is better for snow and slop.
I started running trail races in 2010, beginning at the half marathon distance. I've now completed four 100 mile trail races. In that time, like most trail runners, my "go-to" gear choices have changed a lot. Like others have mentioned, I'd say a good vest/running pack is pretty important. While I've sometimes gone to running primarily with handheld water bottles, the vest is always indispensible for weekend long runs as there is no other way to carry enough water, especially in the summer.
This pic is me at the finish of the Mohican 100 two weeks ago wearing my Nathan Vapor, purchased from REI.