I hope you find this interestIng.
It's from The Everything Wedding Etiquette Book:
This is a fun tradition that's basically a variation on the bouquet toss theme.
Baked inside the usually pink bridesmaids cake is a silver ring tied to a ribbon.
Whichever bridesmaid gets the piece with the ring is the one who will be the first to the altar.
You can either buy the ring and ribbon at a specialty shop and bake it into the cake yourself, or you can order the bridesmaids cake from a bakery."
If you've done this, I'd like to read about it.