Snowboarding is very hard on clothing due to the time spent on snow, too. It'll protect you and make your boardin' baggies last longer. Check out some company links to find technical clothing for snowboarding and you'll find pants and other gear that'll do the trick nicely. Get a helmet, too. They're lightweight, include adjustable venting, and look great.
Injuries when snowboarding are about equal to downhill skiing.
A helmet will pretty much guarantee you don't miss any days boarding due to a concussion or more serious head injury. You probably got a leash with your snowboarding package that's used to keep the board attached to your body so you won't lose control of it when you come off. If you decide not to use it, at least keep it handy in case the ski area has a leash law. Warm and tough waterproof gloves.