To me there is nothing more simple than floating a few blooms in water. Dahlias and Mums are two of my favourites, but experiment with what you have in your garden. Some will last longer than others as petals can become water logged.
Another great thing about floating blooms is that it gets you to dig into your cupboards to find bowls and even glassware you never use. So go dig around and see what you come up with, you may surprise yourself!