I have also seen similar centerpieces that use epsom salts instead of sugar. You could also sprinkle a mix of pearls/gems. Sand (or sugar), faux pearls, a 3 candle. An easy DIY wedding centerpiece idea.
This wedding is lovely and casual! I also love the idea of standing the bridesmaids on the groom's side so that the bride can see their faces! And I really like the idea of just a couple really long tables!