Canyoneering will beat the hell out of your stuff. You'll find the average school bookbag will last a few trips before you destroy the zipper or wear a hole in the bottom. A brand new $160 canyoneering specific pack won't last more than a season or two of hard use. In some cases (or canyons) you might want to optimize for sturdy materials over weight. Bringing a shiny pair of ultralight hiking pants into a sharp Death Valley canyon will end up a $70 disaster by the end of the day.
The suitability of gear is much more important. Bringing a cheap headlamp, jeans and a polo to an after work wet canyon is a sure recipe for disaster. When you're shivering and your light is going out, your friends probably won't feel like you're part of the team. More important than choosing the right materials, is choosing objects that are suitable. That bookbag I mentioned doesn't float (you considered that before tossing it into the swirling pool below, right?)
Desirable attributes for both materials and suitability:
These attributes are typically at the expense of weight - if you're descending a dry canyon then forget about the waterproofing.
Experience and handicaps
Experience comes into play, an expert canyoneer can make the silliest of gear work in a canyon. Some folks could rappel 400 feet wearing a tux and holding a stuffed animal. A beginner's goal should be to handicap themselves as little as possible. An expert should focus on emergency considerations.
Canyoneering ropes should be static, durable, and stay relatively light when wet.
For a comparison of many ropes, see the rope comparison.