Take a look at the ideas on www.positivepromotions.com They are a little pricy but the more you buy the cheaper they get. They have a pin with the American Flag and it reads "Volunteers, Everyday Hereos" many other ones as well.
Quick and simple idea is to take Lifesaver Candies, print labels of Thanks (your choice of wording), and label each. Place them in a basket for each access or personally label each and place in their mailbox or wherever they pick-up assignments, messages, etc.
Keep it simple is always a good train of thought!
Deb,