When creating my jewelry and art I have two main rules:
1) Use what I already have. 2) Only use reclaimed materials.
Sometimes I want something new to work with, so I head to Urban Ore. Urban Ore is a warehouse in Berkeley that is full of reusable goods. One of my favorite things to look for are colorful vinyl records which I can cut up and melt. I have also found most of the packing and wrapping supplies I need. Urban Ore's objective is to keep reusable goods from going to a landfill. "When you shop with us, you are helping keep precious, dwindling, virgin resources safe by reusing what already exists."
Another favorite of mine is the local Goodwill or Salvation Army. When there I mainly hunt for old record sleeves to buy very cheaply to turn into guitar pick art.
Paper Plus Outlet in Berkeley is a fantastic mom and pop shop with all kinds of craft and party supplies. They have unique items, lots of stationary and even jewelry making supplies. Their prices are great and they have a selection that most craft stores don't have.