What you substitute for vanilla-flavored wafers depends on what you are using them for. For instance, if you are just using them as a cookie, any small butter or sugar cookie will work. But for a recipe, you can often substitute them with thin cookies or shortbread cookies.  Alternatively, if you are using them for a pie crust, use crushed Zwieback cookies, chocolate wafers, or graham crackers. Similarly, if you are making banana pudding, try using animal crackers, gingersnaps, shortbread, or chessman butter cookies.