Eh, you shouldnt have to worry too much about preseason workouts. Youre young enough that youll bounce into shape really quick. i would work mostly on leg strengthening and balance as that will help the most when you first jump on your board for the season. Either that or take up longboarding as it keeps you in decent shape and helps with your balancing muscles.
if you want to strengthen your leg muscles, then just walk a mile each day.
walk home from school or join the track team or something.
doesn't take a whole lot to get into shape for snowboarding if you're around our age.
out of curiosity, where do you go to snowboard jake?
Working your legs and core will probably be best. The best leg exercises would be squats or lunges. Google some general leg and core workouts. You probably don't want to be pushing big weights at your age which is good since you're on a budget! Don't leave out the rest of your body altogether though!
Thanks for all the suggestions guys @Zak, I board at paoli peaks, its not that great of a place. The hills are short and the snow sucks, but there isnt really a better option for me right now with living where I do.