Floating Flower Tip - Most flowers float pretty well on their own until they start to pool with water and slowly sink. For a longer lasting centerpiece, use bubble wrap to make little skirts for your flowers.
Scrap Yarn Crochet: Free Yarn Cross Crochet Pattern, make a bit longer and could be a bookmark. (My Nanny, Margaret Lehr Werkheiser, made me one of these out of crochet thread. She added a tassel at the bottom of hers.