I need to train for ski season more..
usually when I train for a climb I do 2 sets of 90 crunches and 2 sets of the plank for 1:00. Then I just time myself on hikes, cut the time by 10-15 minutes each time I go...which if you do enough, can seriously get you in shape.
Other then that just climb a lot of trees,
P.S. nothing conditions you for skiing, like skiing.