Which lens to bring to SKI?

I am going with some friends to vacational skiing this weekend. I normally bring a P&S witih me but this time I want to take better, closer and more "action type" photos.

I haven't brought DSLR with me before and would like to get some advice on what gear I should bring and techniques.

I am a snowboarder at blue/black level.

1) 5D2 - As it has weather sealing I suppose it is okay to bring it up to the mountain, as long as I don't change lens out there?

2) Lens - I want to get some close shots. I have 70-200 2.8 IS, 100-400L, 500 f4 and a 1.4x. Obviously the 500 would give the best AF and IQ. But would it be too cumbersome to carry (I intend to carry a backpack and snowboard down slowly and carrefully). Which lens should I bring?

3) Accessories: Tripod + Wimberley II

4) Would it be dangerous carrying gear on a backpack (and tripod attached) to go to lift and snowboarding down? Or should I just do it at the bottom of the slope?

5) Would a polarizer do any good?

Thank you.