It may cost a lot of money, so start fundraising right away. If you want something really special you can make your own pins. However, if you want to do this do it NOW because it takes a couple of weeks. Contact me for companies to make them for you. As for what you put them on, you can start small and work your way up.
Some people use handkerchiefs, small towels, or washcloths.
Other people make pin books, which are good because they hold your pins, but create the problem that you can't show off your collection all at once. I recommend a simple piece of felt in a dark color. It's sturdy enough to hold a lot of pins, it's nice to touch, and it won't show dirt like a white towel would. The more pins you bring, the more trading you can do. You don't want to run out of pins in the middle of the competition.