Writer Ben Mezrich, of “The Accidental Billionaires’’ and “Sex on the Moon,’’ was on the Rose Kennedy Greenway on Tuesday afternoon so he could be the first local to make a contribution to Candy Chang’s “Before I Die’’ wall, an art experience that kicks off this year’s Fashion’s Night Out. Chang’s art piece is essentially a big black chalkboard decorated with the sentence “Before I die I want to ___.’’ Locals who visit the wall over the next week or so (including Thursday night, which is international Fashion’s Night Out) will be able to fill in the blank with their own aspirations. The wall will be up through Sept. 10. Chang’s Boston display is being sponsored by the Ames. If you want to see what Mezrich wants to do, you’ll just have to stop by.