Traditionally some kalire have seashells or something similar like coconut pieces for a natural look, although these days they are made from metal and beads, and they are meant to be coupled with the red and white bangles that are given to the bride to wear. Although this is more of a custom for Sikh weddings (especially the red and white bangles), the Punjabi side of it is pretty much universal, and also quite sweet: it is tied on the bride's hand by the people she loves as a symbol of sending her off to a happy marriage. Apparently it is also a tradition for the bride to shake her kalire over the heads of unmarried girls and if a piece falls onto any of them, they will be the next to get married (basically the Punjabi equivalent to throwing the westernised bouquet!).
In my experience, I have often seen girls opt to wear the kalire on their mehndi rather than their wedding days, perhaps because sometimes the kalire doesn't suit their wedding outfits (especially if there is a western-look bridal outfit going on), and also perhaps because it's an apt symbol that comes from the people that love them who are present on their mehndi day. Although I must say, I have never seen a bride shaking kalire on top of her friends or family (they might kill her for messing their hair up!), perhaps because not many of us know about this custom. I'm sure many Pakistani and Indian girls from the Punjab side of South Asia will be familiar with this accessory, as it is something that has been present through many years and is just one feature of many which goes back to their roots.