Our certerpieces used sliced limes with flowers on top. They were DIY. In order to make them we purchased 2 square vases, one was slightly smaller than the other, but the same shape. We placed the smaller vase inside the larger one and we lined the space in between with sliced limes. This way they stay put.
We also had a very large vase on our card table that we were going to fill with apples and then flowers on top but the apples kept floating to the top once we added water. So if you are using fruit I recommend having a smaller container for the flowers and placing the fruit in between. We loved our centerpieces and so did out guests and they released a very fresh and suble citrus smell.