The primary metric for the registration and race-packet process is the quantity of paper used. FitPlanet recommends you measure total paper used in the registration process and set an annual reduction target. If you have taken the Pledge of Sustainability you have already committed to reducing or eliminating paper from the pre-event registration process.
The race packet (AKA goodie or swag bag) is another opportunity to reduce paper and waste in general. Measure the total paper contents of the bag and multiply that by the number of bags prepared. By offering sponsors alternate ways to reach runners, such as a virtual goodie bag, you can dramatically reduce paper usage.