I wear a backpack. Even if you are staying on a slopeside condo then they can come in handy.
1. Hydration pack - This is the entire reason I bought a backpack. I get thirsty as heck on the mountain. Powerade+water keeps me hydrated and helps prevent cramping up on the first day out after an entire year of not snowboarding
2. Spare goggles - if you have ever had to ride down a mountain during a blizzard with no eye protection, then you will understand.
3. Chemical warmers - I don't usually need these, but if I get wet enough/chilled enough to need them then they are available.
4. Beanie - Sometimes I like taking off my sweaty balaclava and dont want my (nearly) bald head to freeze.
5. Food - Sometimes I'll have lunch for the entire crew packed. Sometimes just a few nutty bars or cookies.
6. Board carrying - If you've ever hiked 1+ miles in semi-deep powder, then you'll understand why the ability to strap your board to your back is nice.