HEAT oven to 350°F. Coat a 13 x 9-inch baking pan generously with non-stick cooking spray.
COMBINE graham cracker crumbs and butter in a small bowl. Press into the bottom of a prepared pan. Pour sweetened condensed milk evenly over the crumb mixture. Layer with coconut, chocolate chips, M&M candies, sprinkles, and nuts if desired. Press down firmly with a fork.
BAKE 25 to 30 minutes or until lightly browned. Allow to cool on a wire rack for at least one hour. Cut into bars, serve, and enjoy.