I've had the opportunity to volunteer at the Calgary Processing Center a couple times. It is SO much fun. I am from Manitoba, so Calgary isn't exactly "close by", but I've managed to work some volunteer slots into a couple family of trips we've taken over the years. It's overwhelming when you see the amount of volunteers and boxes! A great fun and friendly atmosphere and a way to get some new ideas for your own boxes. :)
This is an old blog post (2007!) but you can read about it if you click here.
If you want to check into volunteering yourself, click this link for more details.