I'm echoing most of what andrewclaus said, but a little reinforcement can't hurt right?
I would definitely bring a water filter, steripen, or at the very least purification tabs. Tap water is safe to drink but there can be long stretches between towns and you don't want to just dip in to the river (giardia risk).
Also, bear spray and rope/carabiners to hang your food are pretty essential. Most campgrounds don't have bear lockers because they assume people have vehicles! Nothing ruins your trip more than having a bear eat all your food (I've had it happen). Also, squirrels, raccoons, and crows can do the same thing. Harder to keep it away from them though
Toilet paper is a very essential and frequently overlooked item. Ditto for any medication you might want. We're a civilized nation, but sometimes towns get sparse.
Where exactly are you planning to go? If you're going anywhere near the mountains (which is kind of unavoidable starting in Vancouver!), you'll probably want a warmer sleeping bag than you might think. I would go with at least a -7 rated mummy bag. This time of year it's already starting to dip down near freezing in the Rockies.