I helped out with a Flat Stanley visit recently and for that class it was NOT about traveling, it was about showing Stanley the place you live. We took him with us for regular daily activities around the city and took pictures of him/us in front of local landmarks, including the subway, etc.. I suggest taking him to work with you and whatever else you do for a day. The kids in the 3rd grade class will benefit just as much from learning about your work and life thru Stanley as they would from some kind of exotic travel. Your cousin must have picked you because s/he thought you had a context worthy of study by 3rd graders. So go with that.