I'm curious about those coins too - they sound way cool!
I like to get those little orange leaf bags they make for people to hang from their trees that look like ghosts. I fill those with fun stuff I buy at the dollar store, and try to include a home-made treat. One year I made my own candles, which was fun but not as inexpensive as buying them at a dollar store. The bags serve as a goodie as well, because they are decorations the guest can use for leaves and hang from their trees and are biodegradable.
Also, another great thing to fill a bag is to get an old-fashioned polariod and take snaps of everyone in their costumes together. It can be another thing to fill their goodie bag at the end of each night, and will make sure the guest never forgets the party!

Leigh Clements
The Mystery Maiden
Shot In The Dark Mysteries.com