I wanted something with a bit of sparkle and for it to be the same for each girl to tie them together (not literally) as their dresses will be different.
I decided on a Swarovski bow charm necklace for each of them (the photo does not do the sparkliness justice). I bought the charms and chains seperately and assembled later (plus a charm for myself to add to a bracelet I already have!)
I plan to give each of the girls their goody bag on the morning of the wedding so their necklaces will be a nice surprise. I've kept them secret so far and have only told them they don't need to worry about jewellery.