The West Coast Trail is notorious for it's wetness. One investment we made prior to the trip last year was a couple of dry bags. These don't show up on my gear-list as I wouldn't normally feel that they are necessary, but they sure gave great peace of mind. They delivered bone-dry down night after night – even after a few mud-pit submersions 🙂
Available from backcountrygear.com starting at $11.95 for the small.