These days the best tool for visualizing math is probably a computer. Nevertheless, I find it helpful/fun/nice-break-from-the-computer to sometimes make physical objects or drawings by hand. The most basic tools are of course a pen and paper, and a lot can be done with just this, especially if you start folding. Here are some other basic supplies I keep in my office:

• Colored pencils/pens
• Cardstock
• String
• Thumbtacks
• Compass
• Straightedge
• Protractor
• Tape
• Scissors

What are some other supplies that are useful to have around?