1) A wagon filled with cookies.
2) A wagon constructed of cookies, similar to the construction of a gingerbread house.
3) A group of people who are all communally engaged in eating cookies.
Definition 1: "I was out jogging yetserday and saw the cookie wagon on Sesame Street. It was probably on its way to the Cookie Monster's."
Definition 2: "I'll bet I could make a cookie wagon better than Mrs. Fields."
Definition 3: "Those look delicious, mind if I hop on the cookie wagon too?"