For shooting yourself doing tricks use a camera designed to take abuse like a GoPro, trying to do tricks while wielding a DSLR is not only dangerous but will ensure you can never push the envelope.
For shooting your friends doing tricks a DSLR with fast telephoto lens is ideal. Try to avoid shooting when the sun is brightest if possible and be mindful of backgrounds as you need the boarder to have separation.
To freeze motion you will want a very quick shutter speed. (unless you get really good and can pan your lens at the exact same speed they are moving, in which case they will be razor sharp and the background will have a motion blur, very hard to do though)
Basically when shooting the image you need your subject (the snow boarder) to be obviously separated from the background. For example compare shooting a boarder with a blue sky background to a cluttered one filled with trees. Basically you want to the boarder to very obviously stand out, whether it is by shooting them against a background that they contrast heavily with or by shooting them with a very narrow depth of field so that the background is out of focus and thus blurry.
Exactly that! ^^ And you can get chest bags for a camera... Falling back you're likely to go on to a pack and crush what ever is in it, falling forwards you're likely to go in to break fall on your forearms keeping your head (and chest) up