Unity Sand Ceremony, Sand mixing, sand blending, or whatever you choose to call it, is a variation of the Unity Candle lighting that has become popular over the years.
In the church ceremony, the bride and groom would each take a candle and light a center candle representing the blending of two individuals (or two families) into one.
For beach weddings, candles and flame just don't work so, we do it with sand.
Some websites are now offering this as a "free" service and use sand taken from the beach and poured into a simple cloth sack.
We think that if a couple wants to spend the time to do it, it should be special, and a sack of sand displayed on their mantle is anything but special. LOL
We have our clients to bring their own implements. Decorative glass vases can be purchased in a variety of styles and a variety of sand colors at most wedding stores and on-line. The colored sand actually makes a nice pattern and display
FYI: The sand has to be very fine and must be dry or it won't pour... hence the sack other websites use. Beach sand doesn't pour well (even into a beer bottle...we've had people do that LOL), and because it's all the same color, it just looks like a jar with sand in it.