When snowboarding you need quite some gear. You can decide to ren it all but some things might be usefull to bring yourself. I bought my own ski suit at the Pull and Bear in Barcelona (see my BCN shopping tip), then when it's warm the only thing you'll be needing for under your suit is a long sleeve t-shirt. If it's colder it is wise to bring some thermic underwear.
Then you need a snowboard or a pair of ski's and ski or snowboard shoes. I borrowed an old snowboard from someone, so I only needed to rent some shoes, but they didn't come very cheap. 5 days was 69 CHF to give you an idea. So please try to borrow them too!!!