"Stones and Rocks DIY Wedding guest book". Guests write messages to bride and groom on rocks with Sharpie instead of signing traditional guest book. This would be cool to put in giant glass vases on either side of the fireplace once the wedding was over.
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.