Preheat oven to 325°F. In medium bowl, combine flour, baking soda and salt. In separate bowl, whisk together oil, buttermilk, eggs, vanilla and rum extract. Stir in sugar, pineapple and, if desired nuts. Add flour mixture; mix well. Pour into prepared pan.
Bake 20-25 minutes or until toothpick inserted comes out clean. Cool 10 minutes in pan on rack; remove and cool completely before decorating.